US President Donald Trump and Ukraine's leader Volodymyr Zelenskyy, in Rome for the funeral of Pope Francis, met one-on-one in a marble-lined Vatican basilica on Saturday to try to revive faltering efforts to end Russia's war with Ukraine.

Zelenskyy said the meeting could prove historic if it delivers the kind of peace he is hoping for, and a White House spokesman called it "very productive".

The two leaders, leaning in close to each other with no aides around them while seated in St Peter's Basilica, spoke for about 15 minutes, according to Zelenskyy's office, which also released photographs of the meeting.

The meeting at the Vatican, their first since an angry encounter in the Oval Office in Washington in February, comes at a critical time in negotiations aimed at bringing an end to fighting between Ukraine and Russia.

Change in tone

In a post on social media platform Telegram, Zelenskyy wrote: "Good meeting. One-on-one, we managed to discuss a lot. We hope for a result from all the things that were spoken about."

He said those topics included: "The protection of the lives of our people. A complete and unconditional ceasefire. A reliable and lasting peace that will prevent a recurrence of war."

Zelenskyy added: "It was a very symbolic meeting that has the potential to become historic if we achieve joint results. Thank you, President Donald Trump!"

In a post on Truth Social after his talks with Zelenskyy in Rome, Trump also said perhaps Russia's President Vladimir Putin "has to be dealt with differently" as he may "not want to stop the war" in Ukraine.

"There was no reason for Putin to be shooting missiles into civilian areas, cities and towns, over the last few days," Trump said in the post.

"It makes me think that maybe he doesn't want to stop the war, he's just tapping me along, and has to be dealt with differently, through 'Banking' or 'Secondary Sanctions?' Too many people are dying!!!"

Their meeting came a day after Putin had told US envoy Steve Witkoff at a Friday meeting in Moscow that he was ready for talks with Ukraine "without preconditions," the Kremlin said Saturday.

No aides in sight

In one photograph released by Zelenskyy's office, the Ukrainian and U.S. leaders sat opposite each other in a hall of the basilica, around two feet apart, and were leaning in towards each other in conversation. No aides could be seen in the image.

In a second photograph, from the same location, Zelenskyy, Trump, British Prime Minister Keir Starmer and French President Emmanuel Macron were shown standing in a tight huddle. Macron had his hand on Zelenskyy's shoulder.

After Trump and Zelenskyy met in the basilica, the two men joined other world leaders outside at the funeral service for Pope Francis, who made the pursuit of peace, including in Ukraine, a motif of his papacy.

Italian Cardinal Giovanni Battista Re, who gave the sermon at the funeral service, recalled how Pope Francis did not stop raising his voice to call for negotiations to end conflicts.

"War always leaves the world worse than it was before: it is always a painful and tragic defeat for everyone," the cardinal said.

A Zelenskyy spokesman had earlier said aides to the two leaders were working on arrangements for a follow-up meeting in Rome later on Saturday. The spokesman subsequently said, after Trump's aircraft took off from Rome, that the second meeting did not happen, citing the presidents' tight schedules.

Differences over territory

Trump, who has been pressing both sides to agree on a ceasefire, said on Friday that there had been productive talks between his envoy and the Russian leadership in Moscow, and called for a high-level meeting between Kyiv and Moscow to close a deal.

Trump had previously warned his administration would walk away from its efforts to achieve a peace if the two sides did not agree on a deal soon.

After a round of shuttle diplomacy this week, differences have emerged between the position of the Trump White House on peace talks and the stance of Ukraine and its European allies, according to documents from the talks obtained by Reuters.

Washington is proposing a legal recognition that Crimea, the Ukrainian peninsula annexed by Moscow in 2014, is Russian territory, something that Kyiv and its allies in Europe say is a red line they will not cross.

There are also differences on how quickly sanctions on Russia would be lifted if a peace deal were signed, what kind of security guarantees Ukraine would have, and how Ukraine would be financially compensated.

Trump and Zelenskyy have had a rocky personal relationship. At their Oval Office meeting, Trump accused the Ukrainian leader of "gambling with World War Three".

Since then, Kyiv has tried to repair relations, but the barbs have continued. Zelenskyy has said Trump was trapped in a "disinformation bubble" that favoured Moscow, while the U.S. leader accused Zelenskyy of foot-dragging on a peace deal and making "inflammatory" statements.

But the two men need each other. Trump requires Zelenskyy's buy-in to achieve his stated ambition of bringing a swift peace between Russia and Ukraine, while Kyiv needs Trump to pressure Moscow into diluting some of the more onerous conditions it has set for a truce.

At the Oval Office meeting in February, a reporter who was present from a conservative U.S. news network accused Zelenskyy of disrespecting the occasion by not wearing a suit.

Zelenskyy, since the start of Russia's full-scale invasion in 2022, has eschewed suits in favour of military-style attire, saying it is his way of showing solidarity with his countrymen fighting to defend Ukraine.

In Rome on Saturday, Zelenskyy again decided against a suit, and instead wore a dark shirt, buttoned up to the neck with no tie, and a dark military-style jacket over the top of that.