US President Donald Trump has said next week's state visit from King Charles and Queen Camilla could "absolutely" help improve relations with the UK.

When asked in a phone interview with the BBC whether the visit could help repair the relationship, Trump said: "Absolutely. He's fantastic. He's a fantastic man. Absolutely the answer is yes."

"I know him well, I've known him for years," he said. "He's a brave man, and he's a great man. They would absolutely be a positive."

The president also spoke about his relationship with UK Prime Minister Keir Starmer, who he said could only "recover" if he changed course on immigration.

The King and Queen will travel to the US for a four-day visit beginning on Monday, and will meet with Trump at the White House.

The King will have a private meeting with the president and also deliver an address to Congress.

After two days in Washington DC, they will travel to New York, Virginia and Bermuda before returning to the UK.

The Foreign Office said the trip will mark the 250th anniversary of US independence, and will celebrate a partnership of "shared prosperity, security and history".

In the interview on Thursday, Trump was also asked about his relationship with UK Prime Minister Keir Starmer.

The two leaders have appeared at odds over the war in Iran, and Sir Keir has faced mounting pressure over his decision to appoint Lord Mandelson as UK ambassador to the US.

In a post on Truth Social on Monday, Trump said Lord Mandelson was "a really bad pick" but the prime minister had "plenty of time to recover".

When asked what he meant by that post, Trump said: "If he opened the North Sea and if his immigration policies became strong, which right now they're not, he can recover, but if he doesn't, I don't think he has a chance."

Trump has repeatedly called on the UK to increase oil and gas extraction in the North Sea.

He has also criticised the UK government and other allies over their response to the Iran war. Trump has said he is "not happy" with the level of support offered by the UK, while Sir Keir has repeatedly said the country will not be drawn into a "wider war".

When the president was asked why he needed allies such as the UK to get involved, he told the BBC: "I didn't need them at all but they should've been there. I didn't need them, obviously."

"We've wiped Iran's military out, he added. "I didn't need anybody."

"I wanted to see whether or not they would be involved," Trump said, describing his calls for support as "more of a test".

Trump was also asked whether his threat, made earlier this month, that "a whole civilisation will die tonight" unless Iran agreed to a deal was about nuclear weapons. The comment was widely condemned, including by the Pope and the head of the UN.

"The other side is dying to make a deal," he said. "So whatever I'm saying or whatever I'm doing, it seems to be working very well."