A top aide to US Vice-President Mike Pence has tested positive for Covid-19 one day after another White House staff member was diagnosed with the virus.
Mr Pence’s press secretary Katie Miller tested positive on Friday, a day after President Donald Trump’s valet.
The White House has begun daily testing for Mr Pence and Mr Trump, and has claimed to be taking “every single precaution to protect the president”.
The US death toll is now over 76,000 and states are beginning to reopen.
Six members of Mr Pence’s team were abruptly taken off his plane, Air Force 2, after it was held on the tarmac outside Washington, DC for over an hour on Friday, as he prepared to travel to Iowa to meet religious leaders.
The staff members had had recent contact with Mrs Miller, according to an unnamed US official cited in the media pool report. The president and vice-president had not.
Mrs Miller is the wife of Trump aide Stephen Miller.
BBC White House correspondent Tara McKelvey
The president has made it clear that he does not like the way that a mask looks on him.
He said last month that he believes wearing a mask would not make a good impression on world leaders and others he meets.
“As I greet presidents, prime ministers, dictators, kings, queens … I don’t see it for myself, I just don’t,” Trump told a journalist.
For some, the president’s refusal to wear a mask is more than a question of style. It is a political statement.
Trump and the other officials at the White House want to give people the impression that the health crisis is under control and that soon the economy will be on back on track.
The decision of the president and others at the White House not to wear masks, writes the Washington Post’s David Nakamura, conveys “a sense of confidence that life, at least for the nation’s most prominent resident, is returning to a semblance of normalcy during the coronavirus pandemic – a visual cue to the public that conditions are improving as Trump pushes to restart sectors of the economy”.
When asked about the possibility of an outbreak in the White House, Mr Trump told reporters: “All you can do is take precautions and do the best you can.”
He also said he was correct not to wear a mask while visiting the World War II memorial in Washington for VE Day, because the elderly veterans there with him were “far away”.
“Plus the wind was blowing so hard and such a direction that if the plague ever reached them, I’d be very surprised,” he added.
Earlier on Friday, White House Press Secretary Kayleigh McEnany defended the measures taken by the White House to keep officials safe.
“We’ve taken every single precaution to protect the president,” Ms McEnany said.
Mr Trump’s Chief of Staff Mark Meadows also told reporters: “This is the safest place you can come to.”