President Donald Trump Wednesday hailed talks between his envoy and Russian President Vladimir Putin on Ukraine as "highly productive" but US officials said sanctions would still be imposed on Moscow's trading partners.

Trump, who had boasted he could end the conflict within 24 hours of taking office, has given Russia until Friday to make progress towards peace or face new penalties.

US envoy Steve Witkoff held "useful and constructive" talks with Russian President Vladimir Putin Wednesday, a Kremlin aide said.

"A quite useful and constructive conversation took place," Putin's aide Yuri Ushakov told journalists, after the three-hour meeting.

Ushakov said the two sides had exchanged "signals" on the Ukraine issue and discussed the possibility of developing strategic cooperation between Moscow and Washington, but declined to give more details until Witkoff had reported back to Trump.

The Kremlin released a video of Putin shaking hands with Witkoff at the start of the meeting.

Trump said on his Truth Social platform that "great progress was made" during the meeting — but minutes later a senior US official said that "secondary sanctions" were still expected to be implemented on Friday.

Ukrainian President Volodymyr Zelensky said he had spoken by phone with Trump after Witkoff visited Moscow.

Witkoff met Putin for around three hours on a last-minute mission to seek a breakthrough in the 3-1/2-year war that began with Russia's full-scale invasion of Ukraine.

Russian investment envoy Kirill Dmitriev, who earlier greeted Witkoff on arrival and strolled with him in a park near the Kremlin, posted on social media: "Dialogue will prevail."

President Zelensky said that Russia seemed "more inclined" to a ceasefire, but details of a potential deal are of great significance and neither Ukraine nor the US should be deceived by Moscow.