STORY: Volodymyr Zelenskiy on Sunday (May 21) likened the destruction of Hiroshima during World War Two to the devastation seen in Ukraine's Bakhmut.
On Saturday (May 20) Russia claimed to have captured the eastern city, which has been the focus of the longest and bloodiest battle of the conflict.
Zelenskiy - in Japan for the G7 summit - denied this.
"They are in Bakhmut, today. Where exactly, I am not going to tell you. But this means that Bakhmut has not been conquered by the Russian Federation today. There can be no other interpretation."
In Hiroshima the Ukrainian president laid flowers at the cenotaph to victims of the world's first atomic bombing of a city.
Photographs of the aftermath reminded him of of Bakhmut and other destroyed Ukrainian cities, Zelenskiy said.
He had earlier, alongside U.S. President Joe Biden, lamented the "tragedy" that had unfolded.
"For today, Bakhmut is only in our hearts. There is nothing in this place ... just a lot of dead Russians."
During that meeting Biden announced announced a $375 million package of military aid, including artillery and armored vehicles, for Ukraine.
He told Zelenskiy the United States was doing all it could to strengthen Ukraine's defense against Russia.
"Together with the entire G7 we have Ukraine's back and I promise we're not going anywhere."
Russian President Vladimir Putin has hailed what he says was a victory for his forces in Bakhmut, describing it as a "liberation" in a statement on the Kremlin's website.
At the G7, leaders of the world's richest democracies, however, said they would not back down in their support for Ukraine.
During the summit Biden told G7 leaders that Washington supports joint allied training programs for Ukrainian pilots on F-16s.
Kyiv has not yet won specific, public commitments for delivery of the fighter jets, but Zelenskiy said he was confident they would.