US President Donald Trump's envoy Steve Witkoff has met with President Vladimir Putin in Moscow at what Trump has said is a key moment in diplomacy to end the war in Ukraine.

Witkoff has emerged as Washington's key interlocutor with Putin as Trump pushes for a deal to end the war, and has already held three long meetings with the Kremlin leader.

Video published by the Kremlin showed Witkoff and Putin shaking hands and exchanging pleasantries before sitting down on opposite sides of a white oval table.

Putin was accompanied by his foreign policy adviser Yuri Ushakov and investment envoy Kirill Dmitriev.

Members of the delegations, led by Russian President Vladimir Putin and US President Donald Trump's envoy Steve Witkoff, attend a meeting in Moscow. – Reuters

Witkoff's latest visit to Moscow comes a day after Trump criticised a Russian missile and drone attack on Kyiv that killed at least 12 people, and posted on social media: "Vladimir, STOP!"

But Trump also said there had been significant progress in peace talks.

"This next few days is going to be very important. Meetings are taking place right now," Trump told reporters.

"I think we're going to make a deal ... I think we're getting very close."

Russian news outlet Izvestia earlier published photographs showing Witkoff strolling in central Moscow with Dmitriev, who has played a prominent role in contacts with the Trump administration.

Ukraine reaffirmed its positions during London talks, Foreign Ministry spokesman Heorhii Tykhyi says. – Reuters

Meanwhile Ukraine's foreign ministry spokesperson said Kyiv's delegation at a meeting with allies in London this week reaffirmed the principles on which talks on ending Russia's war in Ukraine are based, including never recognising any part of Ukrainian territory as Russian.

Spokesman Heorhii Tykhyi told a briefing that the Ukrainian delegation had also ruled out allowing any country to have a veto on what alliances Ukraine can make and would not let restrictions be imposed on its armed forces.

President Volodymyr Zelensky said previously that the talks between Ukrainian and Western officials in London had not been "easy" but were "constructive."

"No third country has the right to veto Ukraine's choice of alliances and partnerships," Tykhyi said.

Ukraine has repeatedly said it wants to join NATO and sees membership as a guarantee against any aggressive action by Russia, which invaded Ukraine in 2022.

Moscow says Ukraine must not join NATO and has called for Ukraine to be demilitarised.

Zelensky reiterated this week that Ukraine would not recognise Russia's occupation of Crimea, which was annexed by Moscow in 2014. He was criticised the next day by US President Donald Trump, who is seeking a quick end to the war in Ukraine.