He said Washington was still pushing for Kyiv to make big territorial concessions to Russia to halt the conflict that started with Moscow's February 2022 invasion and that has killed tens of thousands.

Washington wants only Ukraine to withdraw its troops from parts of the Donetsk region, where it would install a demilitarised buffer between the two armies, Zelensky said.

"They see Ukrainian forces leaving the territory of Donetsk region, and the supposed compromise is that Russian forces do not enter this territory ... which they already call a 'free economic zone'," Zelensky told reporters.

That, he added, remained one of the key points of contention in the talks with the United States that have intensified after Washington drafted a plan to resolve the conflict that was seen as heeding to much of Russia's demands.

"We have two key points of disagreement: the territory of Donetsk and everything related to it, and the Zaporizhzhia Nuclear Power Plant. These are the two topics we continue to discuss," Zelensky told reporters, including from AFP, at a briefing.

He also said that any potential compromise on territory should be decided by a popular vote.

"I believe that the people of Ukraine will answer this question. Whether through elections or a referendum, there must be a position from the people of Ukraine," he told journalists.

Ukraine said on Wednesday it handed over the updated plan for ending the Russian invasion to Washington but said it was not disclosing details of its amendments pending the American side's reaction.