President Donald Trump's national security adviser, Robert O'Brien, has tested positive for coronavirus, the White House has confirmed.

Mr O'Brien, 54, has been self-isolating and working from home.

The aide has mild symptoms and there was no risk of exposure to Mr Trump or Vice-President Mike Pence, a statement said.

Mr O'Brien is the highest-ranking official in Mr Trump's administration known to have tested positive.

It is not clear when he and the president last met, but one administration official said it had not been for "several days". The pair appeared together two weeks ago on a trip to Miami.

The White House statement read: "He has mild symptoms and has been self-isolating and working from a secure location off site. There is no risk of exposure to the president or the vice-president. The work of the National Security Council continues uninterrupted."

Some staff members told CNN they had only learned of the infection on Monday from the media.

One source told Bloomberg that Mr O'Brien had been out of his office for a week and that the adviser had contracted the virus after a family event.

Anyone near the president is tested regularly for Covid-19.

A number of people in and around the administration have tested positive, including a military member who works as a White House valet, Mr Pence's press secretary Katie Miller, and a helicopter squadron Marine.
Who is Robert O'Brien?

Trained as a lawyer, he has had a long diplomatic career working for both Republicans and Democrats. He is believed to be the highest-ranking Mormon member of the Trump administration.

He was picked to replace John Bolton as national security adviser last September, after Mr Bolton left amid a rancorous fallout with President Trump.

Mr O'Brien shares similar views to Mr Trump on a number of issues, including criticism of the UN and opposition to the Iran nuclear deal.

Mr O'Brien travelled to Paris this month to discuss foreign policy issues with European counterparts, and gave a speech in Arizona in June comparing Chinese President Xi Jinping with Soviet leader Joseph Stalin.