This is CNBC's live blog tracking Friday's developments on the war in Ukraine. See below for the latest updates.

Speaking at an event with young entrepreneurs in Moscow, Russian President Vladimir Putin appeared to ominously hint at further territorial expansion.

"It's impossible — do you understand? — impossible to build a fence around a country like Russia. And we do not intend to build that fence," Putin said, according to Sky News.

Meanwhile, Ukrainian President Volodymyr Zelenskyy has said the country's troops are holding on in cities in the Donbas region. This refers to the Donetsk and Luhansk provinces in the easternmost part of Ukraine.

The U.K.'s Ministry of Defense says the Kremlin is struggling to provide basic services to Russian-occupied territories. The ministry has warned the ruined seaside city of Mariupol is at risk of a major cholera outbreak.

Russian central bank chair says effect of sanctions is unclear

The head of Russia's central bank says it's impossible to draw conclusions on the impact of Western sanctions at this stage.

"So far, the effects of the sanctions are less acute than we feared. This also shows the ability of companies to adapt. But it is premature to say that the full effect of the sanctions has manifested itself," Elvira Nabiullina, chair of the Central Bank of Russia, said at a briefing, at which she also announced the lowering of interest rates to their prewar levels.

"The situation is uncertain, the situation is developing and the situation of the structural restructuring of our economy, of its capacity to rebuild, is also a process, so it's premature to draw any conclusions here," Nabiullina said.

She also said Moscow was preparing a possible legal challenge against E.U. sanctions against Russia's central securities depository and measures freezing the settlement of ruble transactions by its E.U.-based counterparts. She did not provide details, but admitted such a challenge "would not be easy."

— Associated Press

Former President Obama calls for long-term international aid for Ukraine

Former U.S. President Barack Obama urged global leaders to sustain support for Ukraine.

"Our support for Ukraine must remain strong, steadfast and sustained until this conflict reaches a resolution," Obama said during an address at the annual Copenhagen Democracy Summit, applauding the Ukrainian people's "historic resistance to Russian aggression."

"They've united to defend not just their sovereignty, but their democratic identity, and their actions have rallied much of the world behind the values of self-determination and human dignity," Obama said.

"Because of the courage and because of this solidarity on display, Vladimir Putin is failing to achieve his aims inside of Ukraine and beyond ... Meanwhile, Russia is cut off from resources and revenue, and many of its best and brightest have left, a blow to its present, but also to its future," he added.

— Amanda Macias

UK defense chief meets Zelenskyy in Kyiv, pledges continued support

British Defense Secretary Ben Wallace has met Ukrainian President Volodymyr Zelenskyy during a previously unannounced visit to Kyiv.

The U.K. defense ministry says Wallace also held talks with his Ukrainian counterpart, Oleksii Reznikov, during the two-day visit this week.

It said Wallace told Zelenskyy that "U.K. support will continue to meet Ukraine's needs as the conflict enters a different phase."

Britain has been one of the biggest donors of military equipment to Ukraine and recently agreed to send rocket launch systems that can target Russian artillery positions in eastern Ukraine.

Western officials say the conflict is becoming a grinding slow-motion war as Russian forces inch forward in their offensive to capture Ukaine's eastern industrial heartland.

— Associated Press

UN says at least 4,339 killed in Ukraine since start of war

The United Nations has confirmed 4,339 civilian deaths and 5,246 injuries in Ukraine since Russia invaded its ex-Soviet neighbor on Feb. 24.

The Office of the U.N. High Commissioner for Human Rights said the death toll in Ukraine is likely higher, because the armed conflict can delay fatality reports.

The international organization 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

Celebrity chef and humanitarian Jose Andres warns U.S. lawmakers of food crisis in Ukraine

Spanish celebrity chef and restaurateur Jose Andres gave U.S. lawmakers an update on the worsening food crisis inside Ukraine.

Speaking via video conference before the House subcommittee on national security, the two-star Michelin chef said that Russian vessels blocking Ukraine's ports will soon trigger a global food shortage crisis.

"I've seen how Russia in a way, very directly is using this war to put extra pressure around the world by creating famines in places that we should not have," said Andres, who founded the World Central Kitchen, a humanitarian organization dedicated to feeding vulnerable communities.

Andres told lawmakers that so far, his organization has distributed more than 40 million meals to more than 475 cities near and around Ukraine.

"We are working with almost 500 restaurants, food trucks and catering companies in eight countries," he said, adding that his organization has set up 42 warehouses to run operations.

"More than 30,000 bags a day are distributed on top of the hot meals," he said.

— Amanda Macias

Pentagon chief Austin warns Chinese counterpart against helping Russia amid war in Ukraine

U.S. Secretary of Defense Lloyd Austin met with Chinese Minister of National Defense Wei Fenghe as Washington repeatedly warns Beijing, the world's second-largest economy, not to help Russia.

Austin told Wei that the U.S. "is watching the situation very carefully and strongly discouraged China from providing material support to Russia for its war in Ukraine," a senior U.S. Defense official told reporters in Singapore traveling with the Pentagon chief.

The two last spoke in April in what was their first known call since Austin ascended to the top office in the Pentagon.

— Amanda Macias

Russia says Brits and Moroccan sentenced to death committed crimes in Donetsk

Russian Foreign Minister Sergei Lavrov has said that the two Britons and one Moroccan sentenced to death on Thursday had committed crimes in the so-called Donetsk People's Republic.

The three men — Aiden Aslin, Shaun Pinner and Saaudun Brahim — fought alongside Ukrainian forces and surrendered to Russian forces weeks ago. They have a month to appeal the decision by the pro-Russia rebel court.

"The processes you mentioned are based on the legislation of the [self-proclaimed] Donetsk People's Republic, because the crimes we are talking about were committed on the territory of the DPR," Lavrov said of the case.

"Everything else is the subject of speculation. I would not want to be getting involved with the work of the judicial and law enforcement system of the Donetsk People's Republic," he added.

The DPR is internationally recognized as part of Ukraine and much of it remains under Ukrainian control.

British Foreign Secretary Liz Truss has called the sentencing a "sham judgment with absolutely no legitimacy."

— Sam Meredith

Ukraine: Putin's invasion remarks show need to discuss Russia's 'immediate de-imperialization'

Ukrainian presidential advisor Mykhailo Podolyak has responded to Putin's remarks in which Russia's leader appeared to hint at further invasions and likened himself to 18th-century czar Peter the Great.

Podolyak said via Twitter that Putin's comments show why it is ineffective to discuss how Russia is "saving face" over its invasion of Ukraine, and instead should prompt a discussion over Russia's "immediate de-imperialization."

— Sam Meredith

'Impossible': Hungary foreign minister rules out Russian gas ban in next round of EU sanctions

Hungarian Foreign Minister Peter Szijjarto says it is not possible for the European Union to impose a Russian gas embargo in its next package of sanctions.

Speaking to CNBC's Charlotte Reed on the sidelines of the OECD's Ministerial Council Meeting in Paris, Szijjarto said: "When we impose sanctions, then we have to make sure that those sanctions are hurting more those against whom we impose the sanctions than ourselves."

"We have to have a very clear position on the war, which we do have, we condemn Russia for this military aggression. We stand with Ukraine. But we have to take into consideration reality as well," he added.

Szijjarto said Russia currently supplies 65% of Hungary's oil demand and 85% of its gas supplies, adding that a lack of available infrastructure means it's not possible for the landlocked European country to swiftly reduce its reliance on Russian hydrocarbons.

The EU agreed late last month to impose a partial embargo on Russian crude in a bid to cripple President Vladimir Putin's war machine. The watered-down deal covers Russian oil brought into the bloc by sea, with an exemption carved out for imports delivered by pipeline.

Szijjarto spoke of his frustration that Hungary had been portrayed as a country reluctant to punish Russia's war in Ukraine after the country opposed a total ban on Russian oil.

When asked about the prospect of the EU targeting Russian gas exports in its next round of sanctions, Szijjarto said: "No, it's impossible."

"If you're not able to import gas from Russia, then the country stops, economy stops, we cannot heat the houses, we cannot run the economy. Our question is who can offer a solution?" he added.

— Sam Meredith

'We are exhausting the enemy': Luhansk governor says fierce street fights continue in Severodonetsk

Serhiy Haidai, governor of the eastern Luhansk province, has said fierce street fighting continues in Severodonetsk as Russian forces battle for control of the city.

"The whole free Luhansk region came under heavy shelling," Haidai said via Telegram, according to a translation.

"Fierce street fights continue in Severodonetsk. We are exhausting the enemy," he added.

— Sam Meredith

Kremlin struggling to provide basic services to Russian-occupied territories, UK says

Russia is struggling to provide basic public services to the population in Russian-occupied territories, with the ruined seaside city of Mariupol at risk of a major cholera outbreak, according to the U.K.'s Ministry of Defense.

"Access to safe drinking water has been inconsistent, while major disruption to telephone and internet services continues. There is likely a critical shortage of medicines in Kherson, while Mariupol is at risk of a major cholera outbreak," the ministry said via Twitter.

"Isolated cases of cholera have been reported since May. Ukraine suffered a major cholera epidemic in 1995, and has experienced minor outbreaks since, especially around the Azov Sea coast — which includes Mariupol," it added. "Medical services in Mariupol are likely already near collapse: a major cholera outbreak in Mariupol will exacerbate this further."

— Sam Meredith

Zelenskyy says strategically important cities in the Donbas are holding on

Ukraine's President Volodymyr Zelenskyy has said the country's forces are holding on to cities in the Donbas region despite sustained pressure from Russian troops.

The Donbas region refers to the Donetsk and Luhansk provinces in the easternmost part of Ukraine. It is a major strategic, political and economic target for the Kremlin.

"Frontlines situation for the day has not seen any significant changes. Sievierodonetsk, Lysychansk and other cities in Donbas, which the occupiers now consider key targets, are holding on," Zelenskyy said in an evening address to the nation, according to a translation.

"We have a certain positive [development] in the Zaporizhia region, where it is possible to thwart the plans of the occupiers. We are gradually moving forward in the Kharkiv region, liberating our land. We keep defense in the Mykolaiv direction."

— Sam Meredith

Putin appears to hint at further invasions, compares himself to Peter the Great

Russian President Vladimir Putin has appeared to hint at further territorial expansion, in remarks likely to set off alarm bells.

"It's impossible — do you understand? — impossible to build a fence around a country like Russia. And we do not intend to build that fence," Putin said at a meeting with young entrepreneurs in Moscow, according to Sky News.

It came as the Russia leader compared himself to Peter the Great on the 350th anniversary of the czar's birth. Putin sought to draw a parallel between the Kremlin's raging onslaught in Ukraine and the former Russian monarch's conquest of the Baltic coast during a war against Sweden in the 18th century.

"When he [Peter the Great] founded the new capital, none of the European countries recognized the territory as Russian. They all recognized it as Swedish territory. The Slavs together with the Finno-Ugric peoples had always lived there, moreover, this territory had been under the control of the Russian state. Same going towards the west — Narva and his first expeditions," Putin said, according to a translation.

"Why did he go there? He went there to take it back and strengthen it, that's what he was doing. Well, it seems it has also fallen to us to take back and strengthen [territories], and if we take these basic values as fundamental to our existence, we will prevail in solving the issues we are facing," he added.

— Sam Meredith

Zelenskyy discusses EU membership with Macron

Ukrainian President Volodymyr Zelenskyy spoke to French President Emmanuel Macron, and they discussed Kyiv's entry into the European Union amid Russia's ongoing war in Ukraine.

In April, Zelenskyy completed the first step in obtaining European Union membership for Ukraine by submitting a lengthy questionnaire.

The two leaders also discussed the latest developments on the ground and additional French security assistance for Ukraine, according to an Elysee Palace readout of the call.

— Amanda Macias

A look at NATO air power and patrols near Ukraine

Since Russia's late February invasion, the NATO alliance has placed approximately 30 military aircraft on patrol over the skies near Ukraine at all times.

"Spanish jets guard Lithuania's airspace and France surveillance planes scan the skies while U.S. bombers train with Allied air forces," wrote NATO spokeswoman Oana Lungescu.

"In order to deter any potential aggression against Allies, NATO is deploying an unprecedented mix of fighter jets, reconnaissance aircraft and support planes," she added.

Here's a look at the airpower the alliance deployed to the region:

— Amanda Macias

Ukrainian troops hold the front line in the Donetsk region

Ukrainian soldiers hold the line in New York in the eastern Donetsk region.

— Gleb Garanich | Reuters

Read CNBC’s previous live coverage here:

Zelenskyy discusses EU membership with Macron; fighting rages in key city of Severodonetsk