Ukraine's Volodymyr Zelenskiy said on Sunday he believed he could salvage his relationship with U.S. President Donald Trump after their explosive meeting in the Oval Office, but that talks needed to continue behind closed doors.

In an extraordinary meeting that was broadcast live on Friday, Trump accused Zelenskiy of being ungrateful for U.S. aid, of showing disrespect to his country and of risking World War Three, casting into doubt Washington's ongoing support for Ukraine.

Zelenskiy, talking to reporters after a summit with European leaders in London on Sunday, said he did not think the U.S. would stop its assistance to Ukraine, because as "leaders of the civilized world" they would not want to help Russian President Vladimir Putin.

However, Zelenskiy said he remained prepared for any challenges that may arise.

"As regards to salvaging the relationship, I think our relationship will continue," he told reporters via a translator after the London meeting.

But he added: "I do not think it's right when such discussions are totally open. ... The format of what happened, I don't think it brought something positive or additional to us as partners."

Zelenskiy added that he remained ready to sign the proposed minerals deal with the United States, and that he believed the U.S. would be ready as well.