King Charles stressed the value and importance of the "indispensable" UK and US partnership in a well-received speech to Congress in Washington DC.

Speaking in the US Capitol, the King warned the two nations had to stand together in a "more volatile, more dangerous" era - and he delivered some hard truths about the need to back Nato.

"We meet in times of great uncertainty, in times of conflict from Europe to the Middle East which pose immense challenges," he told the chamber, filled with US lawmakers.

It was the biggest diplomatic moment of his reign, against a backdrop of deepening political tensions between the US and the UK - and in the end, he got a standing ovation before he'd spoken.

There were about 12 standing ovations in total, as the audience repeatedly interrupted the King's address with loud applause.

It might once have been taken for granted that the US and UK would be partners in defending democratic values.

But after recent tensions there seemed to be no such guarantees - and the King was here to rekindle that alliance, to an audience including US Vice-President JD Vance and political powerbrokers from both Republican and Democrat parties.

The King spelt out the cornerstones to his US audience: there had to be support for Nato, "keeping North Americans and Europeans safe from our common adversaries". There needed to be backing for the "defence of Ukraine and her most courageous people".

Such speeches are written with the Foreign Office, and there was a clear message sent to US President Donald Trump, who has called for more military spending from US allies.

"Our country, in order to be fit for the future, has committed to the biggest sustained increase in defence spending since the Cold War," said the King.

The domed Capitol building looks part-temple and part-courthouse, appropriate for a speech that was strong on moral messages.

"I am inspired by the profound respect that develops as people of different faiths grow in their understanding of each other," said the King, calling for peace, at a time of an unpredictable conflict in Iran and the Middle East.

But in a later speech at the White House state dinner, President Trump seemed to claim that the King supported him in his position on Iran not being allowed to have nuclear weapons - when the UK and the US had already publicly disagreed over Iran.

"We have militarily defeated that particular opponent, and we're never going to let that opponent ever... Charles agrees with me, even more than I do... we're never going to let that opponent have nuclear weapons," Trump told guests at the state dinner.

The King would usually stay out of such political questions.

In response to Trump's comments, a Buckingham Palace spokesperson said the King is "naturally mindful of his government's long-standing and well-known position on the prevention of nuclear proliferation".

This state visit has also brought personal pressures on the King and Queen, in the toxic fall-out from the Andrew Mountbatten-Windsor scandal.

There have been calls for the King and Queen to meet survivors of the sex offender Epstein. That hasn't happened because of concerns about jeopardising the legal process.

The speech made a coded reference to such abuse, not mentioning Epstein by name, but calling for support for "victims of some of the ills that so tragically exist in our societies today".

There was also a reference to the gun attack in Washington DC at the weekend, which has seen a man charged with attempting to assassinate Trump and has raised security in the US capital to an even more intense level.

"Let me say with unshakeable resolve: such acts of violence will never succeed," said the King.