Trump and Zelenskiy are due to hold talks in Washington on Tuesday, Reuters reported.

A Ukrainian source said last week that US and Ukrainian officials had been discussing a proposal for an air ceasefire to take to Russian counterparts as part of a new round of peace talks.

"It is true that this information emerged a few days ago, but so far it is nothing more than media speculation. There are no specific details on this matter, nor are there any specific details regarding any new proposals or suggestions," Kremlin spokesman Dmitry Peskov told reporters.

Peskov also declined to comment on an assertion by Zelensky that Moscow was preparing to receive 30,000 North Korean troops in Russia's Voronezh region.

"I don’t think it’s necessary to comment on them (Zelensky's remarks)," said Peskov. "It's not for Zelensky to talk about our plans."