Donald Trump's special envoy said Russia had agreed to allow the US and Europe to give Ukraine "robust" security guarantees as part of a potential peace deal.

Steve Witkoff told CNN it was agreed at the Alaska summit that the US and Europe could "effectively offer Article 5-like language to cover a security guarantee", referring to NATO's principle that an attack on one member is an attack on all.

Putin has long opposed Ukraine joining NATO, and Witkoff said the arrangement could be an alternative if the Ukrainians "can live with it".

Ukraine's President Volodymyr Zelensky described the US's security guarantee offer as "historic" ahead of talks with Trump and European leaders on Monday.

Speaking ahead of his visit to Washington DC, Zelensky said any guarantee "must really be very practical, delivering protection on land, in the air, and at sea, and must be developed with Europe's participation".

Meanwhile, following a meeting on Sunday of the "coalition of the willing" - a group of nations including the UK, France and Germany that have pledged to protect peace in Ukraine once it is achieved - a No10 spokesman said leaders had commended Trump's "commitment" to providing security guarantees.

The leaders also "re-emphasised the readiness to deploy a reassurance force once hostilities have ceased, and to help secure Ukraine's skies and seas and regenerate Ukraine's armed forces", the spokesman added.

UK Prime Minister Sir Keir Starmer, French President Emmanuel Macron, Chancellor Friedrich Merz of Germany, European Commission President Ursula von der Leyen and Nato Secretary-General Mark Rutte are set to join Zelensky in Washington on Monday.

Macron said the group would challenge Trump on how far he was willing to go in terms of security guarantees.

"If we're not strong today, we'll pay dearly tomorrow," he said, adding the group's plan was to "present a united front".

Witkoff also told CNN on Sunday that Russia had made "some concessions at the table" about territory, noting Donetsk would be part of an "important discussion" on Monday.

It comes after Putin reportedly presented Trump with a peace offer in Alaska on Friday that would require Ukraine to withdraw from the Donetsk region of the Donbas, in return for Russia freezing the front lines in Zaporizhzhia and Kherson.

The BBC's US partner CBS cited diplomatic sources as saying that European officials were concerned Trump may try to press Zelensky to agree to the terms.

Russia claims the Donbas as Russian territory, controlling most of Luhansk and about 70% of Donetsk. It also illegally annexed the Crimean peninsula in 2014, eight years before launching its full-scale invasion of Ukraine.

Zelensky on Tuesday said Ukraine would reject any Russian proposal to give up the Donbas region, warning it could be used as a springboard for future attacks.

He has also pointed to the country's constitution, which requires a referendum before a change in its territory.

Monday's White House meeting will be Zelensky's first since an acrimonious public exchange in the Oval Office in February, when Trump told him to be more "thankful" for US support and accused him of "gambling with World War Three".

Zelensky was then told to leave the White House.

He appeared to reconcile with Trump in April, in what the White House described as a "very productive" 15-minute meeting before they attended Pope Francis's funeral.

Ukraine has also signed a minerals deal that gave the US a financial stake in the country, and Kyiv made it clear they were willing to pay for US arms.

But there will have been concern in Kyiv and other European capitals following the Trump-Putin meeting on Friday.

The Russian president, who is facing an International Criminal Court arrest warrant for alleged war crimes in Ukraine, stepped off his jet and onto a red carpet to be warmly received by Trump, who later said they had a "fantastic relationship".