Donald Trump has said King Charles III will "be very safe" during his state visit to the US, which is due to begin later on Monday.
Further security talks took place between the White House and Buckingham Palace after a gunman gained access to an event attended by Trump in Washington DC on Saturday.
Asked about the security implications for the royal visit, the US president told CBS' 60 Minutes on Sunday that the grounds of the White House, where King Charles will visit, are "really safe".
The King and Queen's programme will go ahead largely as planned, Buckingham Palace said, with the UK government hoping it could ease diplomatic tensions.
The UK's ambassador to the US, Sir Christian Turner, said the visit would be about "renewing and revitalising a unique friendship" between the two countries.
He said Prime Minister Sir Keir Starmer had spoken to Trump on Sunday, and the trip would proceed largely as expected.
The King and Queen privately reached out to the Trumps to give their sympathies after the attack, during which a Secret Service agent was lightly injured and the president and his wife were rushed to safety.
The four-day state visit will begin in Washington DC, with the King and Queen being greeted at the White House by Trump and the First Lady Melania Trump.
The president said on Sunday: "I think it's great, he'll be very safe... the White House grounds are really safe. This area of not very many acres is really safe.
"And he'll be staying here, I believe he's going to a couple of other locations because he's here for a few days.
"He's a great guy. They called him and they are so looking forward to being here. We spoke this morning."
There are British and US flags flying in the streets around the White House, ahead of what will be several days of political theatre.
It will be a charm offensive by the UK, attending ceremonial events in Washington and making a symbolic show of solidarity at the 9/11 Memorial in New York.
For Trump, it will also be a chance to be seen on the world stage next to royalty and might be a welcome diversion from his own political battles. And he told the BBC that he thought the visit could help repair relations with the UK, saying: "Absolutely, the answer is yes."
Sir Christian said the royal visit would emphasise the "shared history, shared sacrifice and common values" of the two countries and would show that the partnership meant both peoples were "safer, richer and happier".
It is understood that diplomats no longer use the phrase the "special relationship", but this visit comes at an unusually difficult time for the US and UK partnership.
Trump has criticised Starmer over not supporting the US in its conflict with Iran, and there have been disagreements between the two allies.
The state visit, which will include events in Washington DC, New York and Virginia, will show that the "partnership ranges well beyond the government of the day", said the ambassador.
Following the event at the White House on Monday, during which the King and Queen will have tea with the Trumps, they will then attend a garden party with guests who have connections to the US and the UK.
State visits are carried out on behalf of the government and Sir Christian identified three strategic priorities - investment, military co-operation and encouraging "people to people" connections, including tourism and education.
But this visit has faced some criticism, including from Lib Dem leader Sir Ed Davey, who called for it to be cancelled, describing the US president as "unreliable".
The diplomatic centrepiece will be the King's speech to the US Congress on Tuesday, in which the King will have to achieve a balancing act between asserting the UK government's positions and also maintaining friendly relations with Trump.
The US president will make his own remarks at a state dinner at the White House.
Trump has remained an enthusiastic fan of the monarchy and in an interview with Fox News on Sunday, he praised King Charles, saying: "He's really a fantastic person and a tremendous representative."
The UK government will be hoping that some of that warmth will translate to the political relationship.
But Labour MP Emily Thornberry, who chairs the Foreign Affairs Committee, said she remained "anxious" about the potential diplomatic implications of the visit.
She told BBC Radio 4's Today programme: "It is a really high-wire act and the president is so unpredictable, you just don't know what he's going to say."
Speaking to Times Radio last week, Reform UK leader Nigel Farage rejected the suggestion Trump could embarrass the King, saying the president "just won't do that", and that he has an "extraordinary respect" for the royals.
Conservative Party leader Kemi Badenoch has also backed the visit, while other opposition parties have been critical of it.
Liberal Democrat leader Sir Ed Davey has repeatedly called for the visit to be cancelled, pointing to Trump's threat of tariffs against the UK, as well as his party's opposition to the war against Iran, describing the president as an "unreliable" ally.
Green Party leader Zack Polanski told BBC 5 Live Breakfast that he "feels sorry" for the King ahead of the trip, and that the UK should seek to improve relations with the US by "taking a sterner line, not by sending a monarch to be paraded".
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