Donald Trump has said the Duke of Sussex was "not speaking for the UK" when he called for the US to show "leadership" on Ukraine - comments which came days before King Charles was due to meet the president.

Speaking during a surprise visit to Kyiv, and without mentioning Trump by name, Prince Harry said the US should "show that it can honour its international treaty obligations – not out of charity but out of its enduring role in global security and strategic stability".

Asked about the remarks, Trump said: "Prince Harry? How's he doing? How's his wife? Please give her my regards.

"I know one thing, Prince Harry is not speaking for the UK, that's for sure. I think I am speaking for the UK more than Prince Harry."

The US president added that he appreciates Prince Harry's advice "very much".

Prince Harry's unannounced trip to Ukraine came days after he left Australia, where he and wife Meghan, both no longer working royals, had visited in a private capacity.

"The United States has a singular role in this story. Not only because of its power, but because when Ukraine gave up nuclear weapons, America was part of the assurance that Ukraine's sovereignty and borders would be respected," Harry said.

The US president did not answer directly when asked if he would invite Harry to dinner during the state visit of King Charles III and Queen Camilla next week.

"He's a friend of mine. We're really looking forward to it. We've spoken and we're going to have a great time," Trump said about the King.

He added that the guests would be people who "love the UK", and that he too loved the UK, before running through a quick list of what he thought the country needed to do.

"I think they made a big mistake on energy. You should open up the North Sea in Aberdeen. You should open it up," he said.

"And the other thing is they've made a big mistake on immigration."

The trip comes during a tense period in US-UK relations, particularly on the question of British involvement in the Iran war.

The US president previously said he was "not happy" with the UK government's decision not to join offensive operations.

Trump has repeatedly publicly criticised Prime Minsiter Sir Keir Starmer, including describing him as "not Winston Churchill" in March following the government's refusal to allow US aircraft to use UK bases for its initial strikes on Iran.

Responding to a question from BBC News, Trump described the King as a "fantastic man".

The BBC has approached the palace and the Foreign Office for comment.