By Olena Harmash and Yuliia Dysa

KYIV (Reuters) -President Volodymyr Zelenskiy said on Tuesday Ukraine was ready for talks with Russia "in any format" once a ceasefire is set, while the Financial Times reported President Vladimir Putin had offered to halt Russia's invasion at the current front lines.

Both sides are trying to demonstrate progress towards ending Russia's war in Ukraine, now well into its fourth year, after U.S. President Donald Trump said he could walk away from efforts to make peace if there is no breakthrough.

"We are ready to record that after a ceasefire, we are ready to sit down in any format so that there are no dead ends," Zelenskiy told reporters in the presidential office in Kyiv.

He stressed that any discussions regarding the terms of a peace deal should only happen once the fighting has stopped and that it would be impossible to agree on everything quickly.

The Ukrainian president said his delegation would have a mandate to discuss a full or partial ceasefire at talks with European and U.S. officials in London on Wednesday in a follow-up to last week's Paris meeting.

At the same time, the White House said Trump's special envoy Steve Witkoff will again travel to Russia later this week to hold talks with Putin.

Citing people familiar with the matter, the Financial Times reported that Putin offered at a meeting with Witkoff in St. Petersburg this month to halt Russia's invasion across the front line and relinquish its claims to full control of four Ukrainian regions.

Russia only partially controls Ukraine's Donetsk, Kherson, Luhansk and Zaporizhzhia regions it claimed as its own during the full-scale invasion. Putin has publicly demanded that Ukraine withdraw its forces from Kyiv-held areas in the regions.

The FT said the proposal was the first formal indication Putin has given since the war's early months that Russia could step back from some of its maximalist demands. It cited European officials briefed on U.S. efforts as saying Russia's apparent concession could be a negotiating tactic.

The Washington Post reported on Tuesday, citing people familiar with the deliberations, that Washington had proposed recognising Russia's annexation of Crimea and freezing the war's front lines as part of a settlement.

The Crimean peninsula, which Russia seized from Ukraine in 2014, is not one of the four regions in Putin's offer reported by the FT.

Zelenskiy has long said Ukraine will not recognise Russia's occupation of Crimea and other territories as that would violate the country's constitution. However, he has also suggested that Ukraine could win back control over the areas diplomatically over time, rather than by military force.

The U.S. presented the proposals to Kyiv at a meeting with Western countries in Paris last week, the Washington Post said.

Other thorny issues that complicate the peace process include the Kremlin's insistence that Ukraine become formally neutral and not join the NATO military alliance.

Ukraine also hopes a foreign contingent will be deployed to ensure the peace settlement is enforced, serving as a security guarantee against any further Russian aggression. Moscow has repeatedly said it would not accept that.

In an apparent change of plan, U.S. Secretary of State Marco Rubio will not attend the talks in London, a State Department spokesperson said on Tuesday, adding that Washington's Ukraine envoy General Keith Kellogg would attend.

Trump and Rubio said last week that Washington could abandon its peace effort unless there was progress within days. Trump on Sunday said that "hopefully" there would be a deal "this week".

Separately, Zelenskiy said he would be ready to meet Trump when they attend the funeral of Pope Francis along with other world leaders this week.

(Reporting by Reuters; Writing by Cynthia Osterman; Editing by Tom Balmforth and Christopher Cushing)

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