Ukrainian President Volodymyr Zelensky on Sunday renewed his plea for talks with his Russian counterpart, taking to US television to say negotiations were the only way to "end this war," AFP reported.

"I'm ready for negotiations with him," Zelensky told CNN show "Fareed Zakaria GPS," referring to Russia's Vladimir Putin.

"I think without negotiations we cannot end this war," the Ukrainian leader said through a translator.

The reiteration of Zelensky's call for peace talks came as he and other Ukrainians accused Russia of committing war crimes after authorities said that Russia had bombed a school sheltering some 400 people in the besieged city of Mariupol.

"Russian forces have come to exterminate us, to kill us," said Zelensky.

Zelensky has spoken of Ukrainians' fierce resistance to the Russian military operations and told Russia that several thousand of its soldiers have died in battle so far.

"If there is just one percent chance for us to stop this war, I think that we need to take this chance... to have the possibility of negotiating, the possibility of talking to Putin," he said.

"If these attempts fail, that would mean that this is a third world war."