US President Donald Trump has said next week's state visit from King Charles III and Queen Camilla could help repair 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 Sir 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 would mark the 250th anniversary of US independence, and would celebrate a partnership of "shared prosperity, security and history".

In the five-minute interview on Thursday, Trump was also asked about his relationship with Sir Keir.

The two leaders have appeared at odds over the war in Iran, and the prime minister 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.

"I make my decisions based on what's in the British national interest and not what other people say or do," Sir Keir said while talking to broadcasters about the president's comments on Thursday.

"That is why I took the decision that we would not be dragged into the war in Iran," he said. "I'm not going to be diverted or deflected from that by what anybody else says."

Trump has also criticised the UK government and other allies over their response to the Iran war. He 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 conflict.

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 from allies 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, the head of the UN and Sir Keir.

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

Towards the end of the phone interview, the president also referenced his multi-billion dollar defamation lawsuit against the BBC.

He is suing over the way a Panorama documentary edited together different sections of a speech he gave before the Capitol riot on 6 January 2021.

Trump said the BBC had to be "very careful" or it could "destroy" its reputation.

The BBC has previously apologised to Trump over the Panorama edit, but rejected his demands for compensation. It has said there is no basis for a defamation claim and filed to dismiss the lawsuit.

"We have said throughout we will robustly defend the case against us," a BBC spokesperson said on Thursday.

Later on Thursday, Trump threatened to hit the UK with a new tariff if it did not drop its 2% digital services tax on big US technology firms.

"We've been looking at it and we can meet that very easily by just putting a big tariff on the UK, so they better be careful," he told reporters in the Oval Office.

BBC News has contacted Downing Street for comment.