This has been CNBC's live blog covering updates on the war in Ukraine. Follow the latest updates here.

Russia has said that the threat of a nuclear war is very significant, as Foreign Minister Sergey Lavrov stressed the risks should not be underestimated. However, he added that there was a danger the risks were being "artificially" inflated.

U.S. Defense Secretary Lloyd Austin called the nuclear war rhetoric "very dangerous and unhelpful," shortly after his visit to Kyiv.

The U.S. also said it plans to send diplomats back to Ukraine as Russia focuses its assault on the eastern and southern parts of the country.

UK removes all tariffs and quotas on imports from Ukraine

The U.K. announced it will remove all tariffs and quotas on goods from Ukraine in its latest move to provide economic support.

"Removing tariffs on key Ukrainian exports including barley, honey, tinned tomatoes and poultry will help Ukrainian businesses and producers when they need it most," the government said in a statement.

The U.K. also banned exports of products and technology that Russia could use to repress the people of Ukraine, such as interception and monitoring equipment.

"The UK will continue to do everything in its power to support Ukraine's fight against Putin's brutal and unprovoked invasion and help ensure the long-term security and prosperity of Ukraine and its people," said International Trade Secretary Anne-Marie Trevelyan.

"We stand unwaveringly with Ukraine in this ongoing fight and will work to ensure Ukraine survives and thrives as a free and sovereign nation," she added.

Last week, the U.K. announced it would raise economic pressure on Russia by banning imports of more products and raising tariffs.

— Chelsea Ong

U.S. diplomats travel back to Ukraine

Members of the U.S. embassy in Ukraine traveled to Lviv to meet with partners including the Ukrainian foreign ministry, the embassy said in a tweet.

"The visit was a first step ahead of more regular travel in the immediate future," the embassy said. "Preparations are underway to resume Kyiv operations as soon as possible."

Secretary of State Antony Blinken previously said U.S. diplomats will be sent back to Ukraine this week to assess how to safely and effectively reopen the embassy in Kyiv.

— Chelsea Ong

UN says Putin agreed 'in principle' to UN and Red Cross involvement in evacuations from Mariupol

The United Nations said Russian President Vladimir Putin agreed "in principle" to the involvement of the U.N. and the International Committee for the Red Cross in evacuating civilians from the Azovstal plant in the besieged Ukrainian city of Mariupol.

A few thousand Ukrainian troops and civilians are holed up in Ukraine's Azovstal steel plant, which Russia has reportedly resumed strikes on. Ukraine has previously accused Russia of blocking efforts to evacuate civilians from Mariupol.

"Follow-on discussions will be had with the United Nations Office for the Coordination of Humanitarian Affairs and the Russian Defence Ministry," the U.N. said of the private meeting on Tuesday between the U.N. secretary-general and Putin in Moscow.

— Chelsea Ong

IAEA visits Chornobyl nuclear power plant 36 years after world's biggest nuclear disaster

IAEA employees visited the Chornobyl nuclear power plant 36 years after the world's biggest nuclear disaster.

Russia's temporary takeover of the Chornobyl site was "very, very dangerous" and raised radiation levels, but they have now returned to normal, the head of the UN atomic watchdog said.

— AFP | Getty Images

U.S. offers $10 million reward for information on six Russian military officers behind malware attack

The U.S. Department of State's Rewards for Justice program is offering a reward of up to $10 million for information leading to the identification or location of six Russian military officers for their role in a malicious cyber campaign targeting U.S. critical infrastructure.

The Diplomatic Security Service program is looking for Yuriy Sergeyevich Andrienko, Sergey Vladimirovich Detistov, Pavel Valeryevich Frolov, Anatoliy Sergeyevich Kovalev, Artem Valeryevich Ochichenko and Petr Nikolayevich Pliskin for their participation in a destructive malware attack.

All six individuals work in the GRU's Unit 74455, also known by cybersecurity authorities as Sandworm Team, Telebots, Voodoo Bear and Iron Viking.

"These individuals were members of the criminal conspiracy responsible for June 27, 2017, destructive malware infection of computers in the United States and worldwide using malware known as NotPetya," the State Department wrote in a release announcing the reward.

"These cyber intrusions damaged the computers of hospitals and other medical facilities in the Heritage Valley Health System in western Pennsylvania, a large U.S. pharmaceutical manufacturer, and other U.S. private sector entities," the release said, adding that the cyber attack cost the U.S. nearly $1 billion in losses.

The new State Department reward comes after members of the "Five Eyes" intelligence-sharing group warned that a malicious attack on U.S. infrastructure could occur as retaliation for the country providing security assistance to Ukraine.

The group urged those responsible for defending critical infrastructure networks "to prepare for and mitigate potential cyber threats—including destructive malware, ransomware, DDoS attacks, and cyber espionage."

— Amanda Macias

Global sanctions will push back Russian economy gains by 20 years, Blinken says

Secretary of State Antony Blinken said that he believes Russians are feeling the effect of multiple rounds of coordinated global sanctions for the Kremlin's war in Ukraine.

"I think what we're seeing is that people increasingly in Russia are feeling the effects of the disastrous decision by Putin to attack Ukraine," Blinken said during testimony before the Senate Committee on Foreign Relations.

"For example, upwards of 600 companies have left Russia, including many of the major consumer brands that we all know and are familiar with," he said, adding, "They can't buy the things they've been used to buying for the last almost 30 years."

The nation's top diplomat said that the gains of the last 20 years are being erased and Moscow's ability to modernize key sectors of its economy is slowing. Despite all of that, Blinken said that he believes Russian President Vladimir Putin still holds large support from his citizens, largely due to disinformation campaigns.

"For now, I think what we're seeing is Russian people to the extent that they're informed continue to support for the most part President Putin," Blinken added.

In the weeks since Russia's invasion of its ex-Soviet neighbor, Washington and its allies have imposed rounds of coordinated sanctions vaulting Russia past Iran and North Korea as the world's most-sanctioned country.

 — Amanda Macias

Civilians take up temporary residence in new 'container towns' in Lviv

Civilians take up temporary residence in new "container towns" in Lviv, Ukraine provided by the Polish government and made available to refugees from eastern Ukraine.

The rooms include beds for four people, storage space for clothing and a small table, with an electric heater.

Meals are provided by the World Central Kitchen charity. Lviv has served as a stopover and shelter for the millions of Ukrainians fleeing the Russian invasion, either to the safety of nearby countries or the relative security of western Ukraine. 

— Getty Images

U.S. intel helped Ukraine protect air defenses, shoot down Russian plane carrying hundreds of troops

As Russia launched its invasion, the U.S. gave Ukrainian forces detailed intelligence about exactly when and where Russian missiles and bombs were intended to strike, prompting Ukraine to move air defenses and aircraft out of harm's way, current and former U.S. officials told NBC News.

That near real-time intelligence-sharing also paved the way for Ukraine to shoot down a Russian transport plane carrying hundreds of troops in the early days of the war, the officials say, helping repel a Russian assault on a key airport near Kyiv.

It was part of what American officials call a massive and unprecedented intelligence-sharing operation with a non-NATO partner that they say has played a crucial role in Ukraine's success to date against the larger and better-equipped Russian military.

The details about the air defenses and the transport plane, which have not previously been reported, underscore why, two months into the war, officials assess that intelligence from U.S. spy agencies and the Pentagon has been an important factor in helping Ukraine thwart Russia's effort to seize most of the country. 

Read the full story here.

 — Ken Dilanian, Courtney Kube, Carol Lee and Dan De Luce, NBC News

Turkey's Erdogan holds a call with Putin

Russian President Vladimir Putin spoke by phone with Turkish President Recep Tayyip Erdogan, one of the few world leaders who maintains good relations with both Moscow and Kyiv.

But the two countries' separate overviews of the call, issued afterwards, gave very different impressions of the conversation.

According to Turkey, Erdogan emphasized how important it was for Russia and Ukraine to continue high level talks like those that Erdogan hosted in Istanbul last month. The Turkish president proposed to Putin that the next talks be held at the leader level, meaning directly between Putin and Ukrainian President Volodymyr Zelenskyy.

But a Kremlin readout downplayed those negotiations, saying Putin and Erdogan also discussed growing trade and economic cooperation between Turkey and Russia, as well as the situation in besieged Mariupol.

— Christina Wilkie

U.S. will send diplomats back to Ukraine this week, Blinken says

Secretary of State Antony Blinken told lawmakers that the U.S. is sending its diplomats back to Ukraine this week.

The nation's top diplomat added that the State Department is also working on plans to reopen its embassy in Kyiv.

"We are sending diplomats back to Ukraine this week and they will begin to assess how we can most effectively and securely reopen the embassy in Kyiv. And without going into too much detail in this setting, I anticipate that we will be in Lviv and then head to Kyiv subject to the president's final decision," Blinken said during testimony before the Senate Committee on Foreign Relations.

"We want to have our embassy reopened and we're working to do that," he added.

On Monday, President Joe Biden announced his plan to nominate Bridget Brink to serve as the U.S. ambassador to Ukraine. Brink, a career diplomat, is currently the U.S. ambassador to the Slovak Republic. 

 — Amanda Macias

U.S. Defense Secretary Austin calls Russian nuclear war rhetoric 'very dangerous and unhelpful'

U.S. Secretary of Defense Lloyd Austin called Russia's recent rhetoric about the potential use of its nuclear weapons "very dangerous and unhelpful."

"Nobody wants to see a nuclear war that nobody can win at. And as we do things, we are always mindful of making sure that we have the right balance and we're taking the right approach," Austin told reporters at a press briefing in Ramstein Air Base in Germany.

"There's always a possibility that a number of things can happen but again, I think it's it's unhelpful and dangerous to rattle sabers and speculate about the use of nuclear weapons," Austin said, following a trip to Ukraine's capital Kyiv alongside Secretary of State Antony Blinken.

Austin's remarks come after Russian Foreign Minister Sergey Lavrov warned that his country's war with Ukraine could escalate into a nuclear one.

Lavrov said late on Monday that the risks of nuclear war are now "very, very significant and should not be underestimated."

 — Amanda Macias

More than 8 million people expected to flee Ukraine by the end of the year, UN says

The United Nations refugee agency expects there to be 8.3 million Ukrainian refugees in neighboring Eastern European countries by the end of the year.

The Geneva-based organization called for $1.85 billion to address the ongoing refugee and humanitarian crisis and to support neighboring countries like Hungary, Moldova, Poland, Romania, Slovakia, Bulgaria and the Czech Republic.

The agency said that so far 5.2 million people have fled Ukraine in the past two months since Russia invaded.

"The human impact and the suffering already caused by this war are staggering. Families have been torn apart, houses and infrastructure have been destroyed, while the trauma of war will have a lasting impact on many of those forced to flee their homes, including women and children who represent some 90% of those forced to flee," said United Nations refugee agency spokesperson Shabia Mantoo in a statement.

"Until we see an end to this war, humanitarian needs will continue to grow and displacement will not cease," Mantoo added.

 — Amanda Macias

Kharkiv residents take shelter in Metro stations

Civilians are seen in a metro station used as bomb shelter in the Saltivka neighborhood of Kharkiv City.

— Anadolu Agency | Getty Images

'We'll fight until we win,' Ukrainian Foreign Minister Kuleba says

Ukrainian Foreign Minister Dmytro Kuleba said his country will fight back against Russia's invasion "until we win."

"We don't have the luxury to make any estimate" about when the war will end, Kuleba told MSNBC's "Morning Joe." He added, "We'll fight until we win because if we lose there will be no Ukraine."

"We will pay the price for the safety of the world and we are ready to do it because it's also the price for our own independence," Kuleba said.

Kuleba said that the war would be over sooner if allies sent more weapons to Ukraine and imposed additional sanctions on Russian oil and gas. He also called for the complete disconnection of all Russian banks from the international financial system.

"This victory may be much closer than anyone might think if we get support on all the weapons, especially heavy weapons," he said, naming U.S. howitzers. "The sooner this is done, the sooner we'll win."

 — Amanda Macias

Watch: U.S. Secretary of State Blinken testifies before Congress

[The stream is slated to start at 10 a.m. ET.]

Germany announces first heavy weapons delivery to Ukraine

Germany announced its first delivery of heavy weapons to Ukraine to help it fend off Russian attacks following weeks of pressure at home and abroad to do so amid confusion over its stance.

— Reuters

UN says 2,729 killed in Ukraine since start of war, warns death toll is likely higher

The United Nations says it has confirmed 2,729 civilian deaths and 3,111 injuries in Ukraine since Russia invaded its ex-Soviet neighbor on Feb. 24.

Of those killed, the U.N. has identified at least 61 girls and 73 boys, as well as 67 children whose gender is unknown.

The Office of the UN High Commissioner for Human Rights said Monday that the death toll in Ukraine is likely higher, citing delayed reports due to the armed conflict.

The international body said most of the civilian casualties recorded were caused by the use of explosive weapons with a wide impact area, including shelling from heavy artillery and multiple launch rocket systems, as well as missiles and airstrikes.

 — Amanda Macias

Sixth round of EU sanctions on Russia coming 'very soon,' energy commissioner says

A sixth round of EU sanctions is set to be imposed on Russia "very soon," the bloc's energy commissioner Kadri Simson told press in Warsaw.

Simson said that the date the sanctions will be enacted has not yet been decided, as any measures would need to be approved by all 27 EU member states. Simson did not specify exactly what the sanctions would target, though the EU has come under pressure for its continued buying of Russian energy resources, providing Moscow with billions in revenues every week.

The bloc has not moved to sanction Russian oil or gas, in large part due to already high fuel prices and staunch opposition to the move by countries that rely heavily on imports of those commodities from Russia, including Germany, Hungary and Austria.

— Natasha Turak

Ceasefire needed as soon as possible, UN chief says

The United Nations' Secretary-General Antonio Guterres has said that a Ukraine ceasefire is needed as soon as possible after meeting Russian Foreign Minister Sergei Lavrov.

Guterres said in Moscow on Tuesday that conditions for a ceasefire in Ukraine should be created as soon as possible, Reuters reported.

"We are extremely interested in finding ways in order to create the conditions for effective dialog, create the conditions for a ceasefire as soon as possible, create the conditions for a peaceful solution", Guterres said at a meeting with Lavrov.

He is due to meet Russian President Vladimir Putin later today.

— Holly Ellyatt

UN secretary general travels to Moscow to meet with Putin amid criticism from Ukraine

United Nations Secretary General Antonio Guterres has traveled to Moscow to meet Russian President Vladimir Putin. The visit is aimed at gaining ground for cease-fires to help fleeing civilians, and trying to involve the U.N. more deeply in brokering mediation efforts between Russia and Ukraine.

It comes after more than 200 former U.N. officials wrote Guterres a letter last week calling on him step in and take a firmer role in conflict resolution, "out of concern for the existential challenge that the United Nations is facing in this historic juncture."

Ukrainian officials have criticized Guterres for visiting Moscow before visiting Kyiv. The U.N. chief is also expected to meet with Russian Foreign Minister Sergey Lavrov before traveling to Ukraine.

"It is simply wrong to go first to Russia," Ukrainian President Volodymr Zelenskyy told press on Saturday. "There is no justice and no logic in this order. The war is in Ukraine, there are no bodies in the streets of Moscow. It would be logical to go first to Ukraine, to see the people there, the consequences of the occupation."

— Natasha Turak

Ukrainian attacks on Russian soil are 'completely legitimate,' UK minister says

Ukraine is justified in carrying out attacks on Russian territory, one U.K. minister has said, following accusations from Moscow in recent days that Ukrainian operators had fired on Russian facilities, including an oil depot near the countries' shared border.

It is "completely legitimate for Ukraine to be targeting in Russia's depth in order to disrupt the logistics that if they weren't disrupted would directly contribute to death and carnage on Ukrainian soil," U.K. Armed Forces Minister James Heappey told Times Radio.

Russia's invasion of Ukraine set off the war, "and in war Ukraine needs to strike into its opponents depth to attack its logistics lines, its fuel supplies, its ammunition depots, and that's part of it," he said.

Large fires ripped through oil depots in Russia's western city of Bryansk on Monday, less than 100 miles from the Ukrainian border. The facility is a major logistical center for Russia's war operations.

Heappey also appeared to emphasize that the West was not responsible for these attacks, despite providing Ukraine with weapons that have the range to reach Russian territory. He pointed out that many countries use arms imported from other countries, saying, "You tend not to blame the country that has manufactured it, but the country that has fired it."

— Natasha Turak

U.K. dismisses Lavrov's 'bravado,' says there's no imminent threat of nuclear war

Britain's armed forces minister has played down Russian Foreign Minister Sergey Lavrov's warning that the war with Ukraine could escalate into a nuclear one.

Lavrov said late on Monday that the risks of nuclear war are now "very, very significant and should not be underestimated" but the remarks were dismissed as "bravado" by U.K. minister James Heappey.

"Lavrov's trademark over the course of 15 years or so that he has been the Russian foreign secretary has been that sort of bravado. I don't think that right now there is an imminent threat of escalation," James Heappey told the BBC Breakfast program on Tuesday.

When asked about whether Russia would use a tactical nuclear weapon, Heappey said he thinks there's a "vanishingly small" possibility of that sort of escalation.

— Holly Ellyatt

City of Kreminna believed to have fallen to Russian forces

The city of Kreminna in the Luhansk region of eastern Ukraine is believed to have fallen to Russian forces, according to the latest intelligence update from the U.K.'s Ministry of Defence on Tuesday.

"The city of Kreminna has reportedly fallen and heavy fighting is reported south of Izium, as Russian forces attempt to advance towards the cities of Sloviansk and Kramatorsk from the north and east," the ministry said has said in an update on Twitter, though it did not give any more details.

Russian forces are likely attempting to encircle heavily fortified Ukrainian positions in the east of Ukraine, the ministry said, adding that Ukrainian forces have been preparing defences in Zaporizhzhia, a city on the Dnipro river in southeastern Ukraine, in preparation for a potential Russian attack.

— Holly Ellyatt

Russia and India were reportedly in talks to restart coking coal trade

Officials from Russia and India met last week in hopes of resolving coking coal supply issues, Reuters reported citing sources.

Russian coking coal exports to Indian steelmakers have stalled since March due to payment methods, a trade source and an Indian government source said, according to Reuters. That's despite New Delhi signing a plan last year to import coking coal from Russia.

Coking coal is essential in the production of steel, and Russia typically supplies about 30% of the coking needs of the European Union, Japan and South Korea.

Russian trade officials are reportedly concerned about the sanctions from the West and requested that India continue with the deal, the sources said.

Indian officials were invited to visit Russia to strategize how to secure smooth shipments of coking coal, sources said, according to Reuters.  

— Chelsea Ong

Risk of nuclear war now 'very, very significant,' Russia's foreign minister says

The risks of nuclear war are now very significant and should not be underestimated, Russia's Foreign Minister Sergei Lavrov told a Russian TV channel on Monday.

"The risks are really very, very significant," Lavrov told Channel One. However, he also added that there was a danger the risks were being "artificially" inflated.

"The danger is serious, it is real, it cannot be underestimated," Lavrov said in comments reported by Russia's Ria Novosti news agency.

— Holly Ellyatt

UK says Ukraine's grain harvest is likely to be about 20% lower than in 2021

Russia's invasion has "significantly" disrupted Ukrainian agricultural production, the British defense ministry said in an intelligence update.

"The Ukrainian grain harvest for 2022 is likely to be around 20 per cent lower than 2021 due to reduced sowing areas following the invasion," the U.K. ministry said.

Reduced grain supply from Ukraine — the world's fourth largest producer and exporter of agricultural goods — would not only cause inflationary pressures and elevate the global price of grain, but also impact global food markets, the ministry said.

Grain prices have surged since the invasion began, and Morgan Stanley expects grain prices to remain above last year's levels till 2023.

"High grain prices could have significant implications for global food markets and threaten global food security, particularly in some of the least economically developed countries," the British ministry said.

— Chelsea Ong

'We want to see Russia weakened,' U.S. Defense Secretary Austin says

Washington wants to see Russia "weakened" as part of its aims in arming and supporting Ukraine, Defense Secretary Lloyd Austin said Monday during a visit to Kyiv, the first such high-level visit from a U.S. official since the war began.

"We want to see Ukraine remain a sovereign country, a democratic country able to defend its sovereign territory. We want to see Russia weakened to the degree that it cannot do the kinds of things it has done in invading Ukraine," Austin told the press.

"It has already lost a lot of military capability, and a lot of its troops, quite frankly. In terms of our — their ability to win, the first step in winning is believing that you can win. And so, they believe that they can win, we believe that they can win, if they have the right equipment."

The visit saw the U.S. pledge more military and diplomatic support to Ukraine as the Russian invasion entered its 60th day.

— Natasha Turak

Schumer expects 'swift, bipartisan' passage of next Ukraine aid bill

U.S. Senate Majority Leader Chuck Schumer said he expected "swift, bipartisan" passage of another bill to aid Ukraine in its fight against Russia once President Joe Biden submits a new funding request.

— Reuters

Mariupol officials say new mass grave found

Officials in the embattled Ukrainian city of Mariupol say a new mass grave has been identified north of the city.

Mayor Vadym Boychenko said authorities are trying to estimate the number of victims in the grave about 10 kilometers (about 6 miles) north of Mariupol.

Satellite photos released over the past several days have shown what appear to be images of other mass graves.

Mariupol has been decimated by fierce fighting over the past two months. The capture of the city would deprive Ukraine of a vital port and allow Moscow to establish a land corridor to the Crimean Peninsula, which it seized from Ukraine in 2014.

— Associated Press

Read CNBC’s previous live coverage here:

The U.S. wants to see Russia 'weakened'; Blinken says Moscow has 'already failed'