U.S. President Donald Trump's national security adviser Robert O'Brien has tested positive for the coronavirus, a source familiar with the situation said Monday.

The White House has said staff is regularly tested for the virus and O'Brien is the most senior official to be found positive amid the pandemic.

O’Brien has been isolating at home and working remotely after apparently contracting the virus at a family event, Bloomberg earlier reported citing unnamed sources.

Politico separately reported it was unclear how O’Brien was exposed to the virus or how much contact he may have had recently with Trump in person.

A U.S. military member, who works at the White House as a valet, tested positive for coronavirus in May as did Vice President Mike Pence's press secretary.