The presidents of four countries on Russia’s doorstep have visited Ukraine in a show of support for the embattled nation after Russian President Vladimir Putin vowed to continue his offensive until its “full completion.”

The presidents of Poland, Lithuania, Latvia and Estonia — all Nato countries that worry they may face Russian attack if Ukraine falls — travelled by train to Kyiv to meet Ukrainian leader Volodymyr Zelensky.

In one of the most crucial battles of the war, Russia said more than 1,000 Ukrainian troops had surrendered in the besieged port of Mariupol, where Ukrainian forces have been holding out in pockets of the city. The claim could not be verified.

Russia invaded on February 24 with the goal, according to western officials, of taking Kyiv, toppling the government and installing a Moscow-friendly one.

In the seven weeks since, the ground advance stalled, Russia has lost potentially thousands of fighters and the war has forced millions of Ukrainians to flee.

The war has also rattled the world economy, threatened global food supplies and shattered Europe’s post-Cold War balance.

US President Joe Biden on Tuesday called Russia’s actions in Ukraine “a genocide” for the first time, saying “Putin is just trying to wipe out the idea of even being a Ukrainian”.

Mr Zelensky commended Mr Biden’s use of the word, saying “calling things by their names is essential to stand up to evil”.

“We are grateful for US assistance provided so far and we urgently need more heavy weapons to prevent further Russian atrocities,” he added.

A view inside the Mariupol theatre damaged during fighting in Mariupol (Alexei Alexandrov/AP)
A view inside the Mariupol theatre damaged during fighting in Mariupol (Alexei Alexandrov/AP)

The European leaders visiting Ukraine delivered “a strong message of political support and military assistance”, Lithuanian President Gitanas Nauseda said.

Mr Nauseda, Estonian President Alar Karis, Poland’s Andrzej Duda and Egils Levits of Latvia also planned to discuss investigations into alleged Russian war crimes, including the massacre of civilians.

Mr Nauseda said the leaders visited Borodyanka, one of the towns near Kyiv where evidence of atrocities has been found.

“This is where the dark side of humankind has shown its face,” he wrote on Twitter. “Brutal war crimes committed by the Russian army will not stay unpunished.”

An expert report commissioned by the Organisation for Security and Cooperation in Europe found “clear patterns of (international humanitarian law) violations by the Russian forces in their conduct of hostilities.” The report was written by experts selected by Ukraine and published on Wednesday by the Vienna-based organisation that promotes security and human rights.

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(PA Graphics)

The report said that there were also violations by Ukraine but concluded those committed by Russia “are by far larger in scale and nature”.

Ukraine has previously acknowledged that there could be “isolated incidents” of violations and has said it would investigate.

Mr Putin, however, has denied his troops committed atrocities, and on Tuesday insisted Russia “had no other choice” but to invade, saying the offensive aimed to protect people in parts of eastern Ukraine and to “ensure Russia’s own security”.

He vowed it would “continue until its full completion and the fulfilment of the tasks that have been set”,

He insisted Russia’s campaign was going as planned despite a major withdrawal after its forces failed to take the capital and suffered significant losses.

Russian President Vladimir Putin (Evgeny Blyatov/AP)
Russian President Vladimir Putin (Evgeny Blyatov/AP)

Following those setbacks, Russian troops are gearing up for a major offensive in the eastern Donbas region, where Moscow-allied separatists and Ukrainian forces have been fighting since 2014, and where Russia has recognised the separatists’ claims of independence.

Military strategists say Moscow believes local support, logistics and the terrain in the region favour its larger, better-armed military, potentially allowing Russia to finally turn the tide in the war.

Britain’s Ministry of Defence said on Wednesday that “an inability to cohere and coordinate military activity has hampered Russia’s invasion to date”.

Western officials say Russia recently appointed a new top general for the war, Alexander Dvornikov, to try to get a grip on its campaign.

A key piece to that campaign is Mariupol, which lies in the Donbas and which the Russians have besieged and pummelled since nearly the start of the war.

Ukrainian presidential adviser Mykhailo Podoliak tweeted that the city’s defenders were short of supplies but were “fighting under the bombs for each metre of the city”.

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Refugees walk after fleeing the war from neighbouring Ukraine at the border crossing in Medyka, southeastern Poland (Sergei Grits/AP)

Russian Defence Ministry spokesman Igor Konashenkov said 1,026 troops from the Ukrainian 36th Marine Brigade had surrendered at a metals factory in the city. It was unclear when the surrender occurred or how many forces were still defending Mariupol.

Russian state television on Wednesday broadcast footage that it said was from the port city showing dozens of men in camouflage outfits walking with their hands up and carrying others on stretchers or in chair holds.

One man held a white flag on a staff in one hand and the handle of a stretcher in another. In the background was a tall industrial building with its windows shattered and its roof missing, identified by the broadcaster as the Iliich metalworks.