The King and Queen's state visit to the United States will be about "renewing and revitalising a unique friendship", says the UK's ambassador, Sir Christian Turner.

The royal visitors, arriving on Monday, were already facing a diplomatic challenge with political tensions between the US and the UK.

But the shooting incident in Washington DC at the weekend, at an event attended by President Trump, added another layer of security concerns.

The UK ambassador said the Prime Minister, Sir Keir Starmer, had spoken to President Trump on Sunday, and that the trip would be going ahead largely as planned.

King Charles and Queen Camilla had privately reached out to the Trumps to give their sympathies after the attack.

After US and UK talks over security, it was decided the trip should continue, with only a few modifications to minimise risks.

The four-day state visit will begin in Washington DC, with the King and Queen being greeted at the White House by President Trump and the First Lady, Melania Trump.

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, with attendance at ceremonial events in Washington and a symbolic show of solidarity at the 9/11 Memorial in New York.

For President 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's 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.

President Trump has criticised Sir Keir 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 critics, including 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 strike a balance between asserting the UK government's positions and maintaining friendly relations with President Trump.

President Trump will make his own remarks at a state dinner at the White House.

The US president has remained an enthusiastic fan of the monarchy, and in an interview with Fox News on Sunday, he praised King Charles: "He's really a fantastic person and a tremendous representative."

The UK government will be hoping that some of that warmth will translate into a stronger political relationship.