"We know this history. We know what Russian occupation means," said Polish President Andrzej Duda.
The presidents of four countries on Russia's doorstep visited Ukraine on Wednesday and underscored their support for the country, demanding accountability for what they called war crimes carried out by Russian forces.
The visit by the presidents of Poland, Lithuania, Latvia and Estonia was a strong show of solidarity from the countries on NATO's eastern flank, three of them like Ukraine once part of the Soviet Union.
The leaders travelled by train to Kyiv to meet with their counterpart Volodymyr Zelenskyy and visited Borodianka, one of the nearby towns where evidence of atrocities was found after Russian troops withdrew to focus on the country's east.
"The fight for Europe's future is happening here," Lithuanian President Gitanas Nauseda said, calling for tougher sanctions, including against Russia's oil and gas shipments and all the country's banks.
Russia invaded on 24 February with the purported goal of taking the capital, toppling the government and installing a Moscow-friendly one, but the advance stalled and Russia lost an estimated thousands of troops.
The conflict has killed untold numbers of Ukrainian civilians and forced millions more to flee. It also has rattled the world economy, threatened global food supplies and shattered Europe's post-Cold War balance.
Appearing alongside Zelenskyy in an ornate room in Kyiv's historic Mariinskyi Palace on Wednesday, Nauseda, Estonian President Alar Karis, Poland's Andrzej Duda and Egils Levits of Latvia reiterated their commitment to supporting Ukraine politically and with military aid.
"We know this history. We know what Russian occupation means. We know what Russian terrorism means," Duda said, adding that those who committed war crimes and those who gave the orders should be held accountable.
"If someone sends aircraft, if someone sends troops to shell residential districts, kill civilians, murder them, this is not war," he said. "This is cruelty, this is banditry, this is terrorism."
Russian President Vladimir Putin has denied his troops committed atrocities, saying on Tuesday that Moscow "had no other choice" but to invade and 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 troops are now 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 recognized the separatists' claims of independence.