A senior U.S. negotiator on Monday welcomed weekend talks in Moscow and Kyiv, saying the discussions could pave the way for a new round of three-way negotiations aimed at ending the Russia-Ukraine war.

"Substantive progress was made, including movement on scheduling additional trilateral talks," U.S. Special Envoy Steve Witkoff wrote on X.

Witkoff, a business ally of President Donald Trump, traveled to Russia and Ukraine over the weekend alongside negotiating partner Jared Kushner, who is Trump's son-in-law.

Sunday's appearance in Kyiv was their first visit to the Ukrainian capital.

A senior Ukrainian official told AFP on Sunday that the two envoys had brought new and "more effective" proposals on ending the war, but Ukrainian President Volodymyr Zelensky warned that fighting appeared likely to continue into the winter.