The Polish and Baltic presidents on Wednesday visited the Ukrainian town of Borodyanka not far from Kyiv, with Lithuanian President Gitanas Nauseda saying it was "permeated with pain and suffering".
"It is hard to believe that such war atrocities could be perpetrated in 21st-century Europe, but that is the reality. This is a war we must win," Nauseda said in a statement.
"The place is permeated with pain and suffering. Civilian Ukrainians were murdered and tortured here, and residential homes and other civilian infrastructure were bombed."
Poland had announced earlier that Nauseda and his fellow heads of state -- Polish President Andrzej Duda, Estonia's Alar Karis and Latvia's Egils Levits -- had met in the Polish city of Rzeszow near the Ukraine border before boarding a train for Kyiv.
The Polish president's office later tweeted a photo of their meeting with Ukrainian President Volodymyr Zelensky.
"Our goal is to show support to President Zelensky and the defenders of Ukraine in a decisive moment for this country," Polish presidential adviser Jakub Kumoch said in a statement.
German President Frank-Walter Steinmeier visited Poland on Tuesday and said he had planned to go on to Ukraine but was turned down.
"I was prepared to do this, but apparently, and I must take note of this, this was not wanted in Kyiv," he told reporters on Tuesday.
Steinmeier, a former foreign minister, is facing criticism at home and abroad for his years-long detente policy towards Moscow, which he has since admitted was a mistake.