Top US virus expert Dr Anthony Fauci, a member of the Covid task force, said it was clear there was a “superspreader event” at the White House.
When asked on CBS News radio about the White House outbreak, Dr Fauci said “the data speak for themselves”.
The comments come as President Donald Trump says he has recovered and is keen to get back on the campaign trail with less than a month to the election.
Critics say the White House has avoided questions on Mr Trump’s health.
CBS News Radio White House Correspondent Steven Portnoy on Friday asked what Dr Fauci, a veteran health official, thought of the White House’s reluctance to insist on mask-wearing and social distancing as virus precautions, and instead rely on regular testing.
“The data speak for themselves – we had a superspreader event in the White House, and it was in a situation where people were crowded together and were not wearing masks.”
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Dr Fauci also noted experts have been recommending mask-wearing for the last six months.
An event at the White House, celebrating the president’s nomination of Amy Coney Barrett as a Supreme Court judge on Saturday 26 October, is thought to be the root of the localised outbreak, as many attendees have since tested positive.
Earlier on Friday, a White House spokeswoman said the president wanted to return to the campaign trail this weekend.
But an administration official later said Mr Trump was unlikely to travel so soon because the logistics of organising events at short notice was problematic. An appearance is more likely on Monday, they said.
The president is also set to have a televised “medical evaluation” on Fox News on Friday evening.