White House staff have been ordered to wear masks when entering the West Wing after two aides tested positive for coronavirus.
The White House personnel office has said that staff must cover their faces at all times except when seated at their desks, socially distant from colleagues.
The directive comes after an aide for Vice-President Mike Pence and a valet for President Trump fell ill.
Mr Trump said he required the policy.
Appearing without a mask in the Rose Garden for a press briefing on Monday, however, the president claimed he did not need to follow the directive because he kept “far away from everyone”, and played down the White House infections.
“We have hundreds of people a day pouring into the White House” each day, he said. “I think we’re doing a good job containing it.”
Three members of the White House coronavirus task force went into self-isolation for two weeks after possible exposure to the illness.
They include Dr Anthony Fauci, who has become the public face of the fight against the virus in the US.
Mr Pence’s press secretary Katie Miller, the wife of Trump aide Stephen Miller, tested positive for the virus on Friday.
Her diagnosis came after a valet for US President Donald Trump was also confirmed to have the illness.
Mr Trump shrugged of the White House spread, saying it was “basically one person” who had contracted the virus and that people who were in contact had since tested negative.