Earlier this month, Trump said he had given Moscow 50 days to reach a peace deal or face what he said would be "very severe" economic sanctions during a visit to Washington by NATO Secretary General Mark Rutte.

US President Donald Trump said on Monday he is to reduce the 50-day deadline he previously set for Russia to agree to a peace deal in Ukraine, highlighting his growing frustration with the ongoing all-out war, now well into its fourth year.

Trump said the new deadline for Putin to agree to a deal would be "10 or 12 days."

"I'm disappointed in President Putin," Trump said in comments alongside UK Prime Minister Keir Starmer in Scotland.

"I'm going to reduce that 50 days that I gave him to a lesser number because I think I already know the answer what's going to happen."

"I've spoken to President Putin a lot, I've gotten along with him very well," he said, adding that Putin "goes out and starts launching rockets into some city, like Kyiv, and kills a lot of people in a nursing home or whatever, you have bodies lying all over the street."

The US president, who boasted on the campaign trail several times that he could end Russia's war in Ukraine within a day, said he and Putin have been close to reaching a ceasefire deal five times, but a final agreement has remained elusive.