This comes amid growing speculation that Russia might be willing to halt its invasion along current front lines in return for significant concessions.

The pace of diplomatic efforts to end the war is quickening but there is little clarity about where they are heading or whether they will succeed.

On Tuesday evening, Rubio spoke to Lammy about what he hoped would be “substantive and good technical meetings”.

Lammy himself called the conversation “productive”, taking place ahead of a “critical moment for Ukraine, Britain and Euro-Atlantic Security” as “talks continue at pace”.

The US secretary of state said he would reschedule his trip to the UK in the coming months, posting on X: “I look forward to following up after the ongoing discussions.”

On Wednesday morning, the UK Foreign Office confirmed talks between foreign ministers had been postponed.

“Official level talks will continue but these are closed to media,” the statement said.

The White House said Witkoff would travel to Moscow this week for his fourth meeting with Russian President Vladimir Putin.

All this comes amid a report in the Financial Times that Russia might be ready to halt its invasion along current front lines and give up some territorial ambitions in return for US recognition of Russian sovereignty over Crimea.

Zelensky said no such proposals had been shared with him and he rejected recognising Crimea as Russian territory.

“Ukraine does not legally recognise the occupation of Crimea. There’s nothing to talk about,” he said during a news briefing on Tuesday night.

Speaking to BBC Radio 4’s Today programme, Yuriy Sak, an adviser to Ukraine’s Ministry of Strategic Industries, said it is “not productive to discuss” such reports but added it is “naïve” to expect Ukraine to change its position on “non-negotiable” issues such as Crimea.

Sak added Ukrainian negotiators would attend the London meeting on a “very clear, narrow mandate” to achieve a ceasefire that will “pave the way for further talks”.

Putin unilaterally called a temporary ceasefire for the Easter weekend but UK Defence Secretary John Healey told the House of Commons on Tuesday that British military intelligence had found no evidence of a let-up in attacks.

“While Putin has said he declared an Easter truce, he broke it,” he said. “While Putin says he wants peace, he has rejected a full ceasefire and while Putin says he wants to put an end to the fighting, he continues to play for time in the negotiations.”

Healey added that he could “confirm Russian military progress” was “slowing” while the country continued to “pressure Ukraine on a number of fronts”.

On Wednesday morning, nine people were killed in the Ukrainian city of Marhanets after a Russian drone hit a bus carrying workers.

Officials say this is the latest in a wave of attacks targeting civilian infrastructure in several regions of Ukraine.

It is estimated that hundreds of thousands of people have been killed or injured on all sides since Russia invaded Ukraine on 24 February 2022, and nearly seven million Ukrainians are currently listed as refugees worldwide.

The conflict goes back more than a decade, to 2014, when Ukraine’s pro-Russian president was overthrown. Russia then annexed Crimea and backed militants in bloody fighting in eastern Ukraine.