This is CNBC's live blog tracking developments on the war in Ukraine. See below for the latest updates.
U.S. President Joe Biden on Monday made a surprise visit to Kyiv, meeting with Ukrainian leader Volodymyr Zelenskyy and reiterating his administration's support for Ukraine as Russia's full-scale war on the country nears its one-year anniversary.
Biden announced new weapons deliveries and upcoming sanctions against Russia before departing after roughly five hours and traveling to Poland.
Meanwhile, an air raid warning was activated for all of Ukraine. Heavy fighting continues in Bakhmut and other parts of Ukraine's south and east, as EU leaders work on ways to improve the efficiency of procuring weapons for the country.
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Biden returns to Poland
President Joe Biden has returned to Poland after his surprise visit with Ukrainian President Volodymyr Zelenskyy in Kyiv.
Money Report
After he left the U.S. Embassy in Kyiv, Biden's motorcade took him to the Kyiv-Pasazhyrsky railway station, where he departed the Ukrainian capital city, according to a pool report. Biden had arrived at the same station in the morning after an approximately 10-hour train ride from Poland.
– Mike Calia
Moscow was notified about Biden trip ahead of time
The White House told the Kremlin ahead of time that President Joe Biden would visit Ukraine, according to a top administration official.
"We did so some hours before his departure for deconfliction purposes. Because of the sensitive nature of those communications I won't get into how they responded or what the precise nature of our message was," national security advisor Jake Sullivan said, according to NBC News.
Biden took a 10-hour train ride from the Polish border into Kyiv, a source familiar with the matter told NBC.
– Mike Calia
Sweden says Russian threat has grown
According to Swedish military intelligence, the Russian threat to Sweden's security has grown, Reuters reported.
"The European Security Order as we know it has ceased to exist," Lena Hallin, head of the Swedish Military Intelligence and Security Service, told a news conference Monday. "And with that the risks for Swedish security have also increased."
She said she expects more of a buildup from Russia, particiarly as Sweden and Finland have applied for NATO membership. But she also thinks Russia wants to avoid a conflict with NATO.
– Mike Calia
King Charles III meets Ukrainian troops training in the UK
Britain's King Charles III met with Ukrainian troops training with British forces in Wiltshire, southern England. He also met with instructors from Australia, Canada, Norway, Sweden, Finland, Denmark, the Netherlands, Lithuania, and New Zealand.
The Ukrainian recruits are partaking in a five-week basic training course with international instructors before returning to Ukraine for combat.
Accompanying the king was Gen. Sir Patrick Sanders, chief of the general staff of the British Army.
— Natasha Turak, Getty Images
Russian state TV channel launches countdown to Putin's speech Tuesday
Russian state TV channel Rossiya 24 began a countdown to President Vladimir Putin's speech to the nation's federal assembly tomorrow. Highly anticipated as it comes just days before the one-year anniversary of Russia's full-scale invasion of Ukraine, the speech is expected to project force and resolve to continue the war.
Some analysts have said that President Joe Biden's surprise visit to Kyiv today has raised the stakes for Putin and may influence him to make his speech "even tougher," Valerie Hopkins of the New York Times wrote on Twitter.
— Natasha Turak
Sweden praises 'welcome message' from Turkey on restarting NATO talks
Sweden says news from Turkey that it is open to restarting NATO membership talks, one month after a far-right wing Quran burning demonstration in Stockholm caused a major rupture between the countries, is a "good and welcome message."
"Of course I am aware that my colleague, [Turkish] Foreign Minister Mevlut Çavusoglu has announced that they are ready to restart the discussion with Sweden, and we are obviously ready to do so," Swedish Foreign Minister Tobias Billstrom told press from Brussels.
"It is a good and welcome message from Turkey ... We will start with restarting [talks], and that's the message that's been given today," he said.
It's not clear what will happen next, but doubts are high among political analysts as to whether Turkey will make any significant moves on green-lighting Sweden or Finland's NATO accession before Turkey's general election on May 14.
Sweden and Finland both presented their formal applications to join NATO in May of 2022, abandoning their historic position of non-alignment in the wake of Russia's full-scale invasion of Ukraine. Approval from all 30 current members of the alliance is required to accept a new member. Turkey and Hungary are the only remaining member states yet to approve the Nordic states' bids.
— Natasha Turak
Zelenskyy: 'Thankful to the U.S. for standing with Ukraine'
Ukrainian President Volodymyr Zelenskyy expressed his thanks to the U.S. for its support in spoken remarks and via social media, calling President Joe Biden's visit "historic" and "brave."
"I welcomed POTUS in Kyiv as Russian full-scale aggression approaches its one-year mark," Zelenskyy wrote via Twitter. "I am thankful to the U.S. for standing with Ukraine and for our strong partnership. We are determined to work together to ensure Ukraine's victory."
— Natasha Turak
Biden departs Kyiv after 5-hour visit
President Joe Biden has left Kyiv after a five-hour surprise visit to the Ukrainian capital, according to reports. His next stop, according to his public schedule, is Poland.
— Natasha Turak
Biden in Ukraine: 'Americans stand with you, the world stands with you'
President Joe Biden expressed America's support for Ukraine in a speech at Kyiv's Mariinsky Palace, standing next to his Ukrainian counterpart Volodymyr Zelenskyy.
"One year later, Kyiv stands," Biden said, recalling widespread beliefs in February of 2022 that Russia's invading forces would take the Ukrainian capital.
"Ukraine stands. Democracy stands. The Americans stand with you, and the world stands with you," he said.
He added that Russian President Vladimir Putin's "brutal and unjust war" is not yet won, and warned of "very difficult days and weeks and years ahead."
Biden said Putin's "war of conquest is failing" and that "he's just been plain wrong" on whether the West would come together to back Ukraine.
"Freedom is priceless," he said, pledging enduring support for Ukraine. "It's worth fighting for for as long as it takes. And that's how we're going to be with you."
— Natasha Turak
Biden, in Kyiv, reiterates support for Ukraine, announces new weapons deliveries
U.S. President Joe Biden is in Kyiv to reiterate American solidarity and support as Russia's full-scale war against the country nears its one-year mark, a White House statement on the visit said. It also outlined new weapons deliveries for Ukraine.
"As the world prepares to mark the one-year anniversary of Russia's brutal invasion of Ukraine, I am in Kyiv today to meet with President Zelenskiy and reaffirm our unwavering and unflagging commitment to Ukraine's democracy, sovereignty, and territorial integrity," the statement read.
"Today, in Kyiv, I am meeting with President Zelenskiy and his team for an extended discussion on our support for Ukraine," it said. "I will announce another delivery of critical equipment, including artillery ammunition, anti-armor systems, and air surveillance radars to help protect the Ukrainian people from aerial bombardments."
— Natasha Turak
EU calls for buying arms for Ukraine jointly to improve efficiency
Estonian leaders and EU foreign affairs chief Josep Borrell are calling for a more uniform approach to buying weapons for Ukraine that would see allies making arms purchases jointly rather than separately. This would increase efficiency and speed up procurement, officials said.
"I completely agree with the Estonian prime minister's proposal, we are working on that and it will work," Borrell said of the proposal, which first came from Estonia.
Still, he warned, it wouldn't meet Ukraine's need for arms quickly enough.
"This cannot be solved by going into joint procurement ... because any procurement that comes to the market will come at the end of a queue of a long list of orders already passed by the member states."
"We have to use what member states have," Borrell added, noting that the urgency was such that EU members need to take from existing arms stocks.
— Natasha Turak
U.S. President Biden makes surprise visit to Kyiv days before one-year mark of Russian invasion
U.S. President Joe Biden arrived in Kyiv in a surprise visit just days before the one-year mark since Russia launched its full-scale invasion of Ukraine on Feb. 24, 2022.
"It is confirmed! Joe Biden spotted in Kyiv this morning. This is a big deal and a historic visit of POTUS," Olga Tokariuk, a Ukraine-based journalist, posted to Twitter.
Biden will be meeting with Ukrainian President Volodymyr Zelenskyy. His public itinerary said he would be traveling to Poland, but he arrived in the Ukrainian capital first.
— Natasha Turak
Air raid warnings sound over all of Ukraine
An air raid warning has been activated for all of Ukraine, local media report. The warning came amid rumors of a high-profile politician's visit to the country, which many suspected could be U.S. President Joe Biden.
"Speculations about the visit of some highest-ranking Western official to Kyiv today as roads in the centre of Ukrainian capital are closed to traffic and Ukrainian foreign minister cancels his trip to Brussels this morning," Ukrainian journalist Olga Tokariuk wrote on Twitter. "The US president Biden expected in Warsaw today."
— Natasha Turak
Russian forces likely suffering high casualties in east, south Ukraine: UK
Russia is likely suffering high casualties among its forces fighting in south and east Ukraine as grinding offensives continue in Bakhmut and other areas, the U.K.'s Ministry of Defence believes.
"Russia continues to pursue several offensive axes in eastern Ukraine: Vuhledar, Kremina, and Bakhmut," the ministry wrote in its daily intelligence update on Twitter.
"Casualties reportedly remain high, particularly in Bakhmut and Vuhledar. Specifically, the 'elite' 155th and 40th Naval Infantry Brigades have sustained very high losses in Vuhledar and are likely combat ineffective."
It added that Russian forces "are likely under increasing political pressure as the anniversary of the invasion draws near," and that Russia may likely "claim that Bakhmut has been captured to align with the anniversary, regardless of the reality on the ground."
— Natasha Turak
