US President Joe Biden has tested positive for Covid-19 and is isolating at the White House.
The 79-year-old, who is fully-vaccinated and has twice received booster jabs, is experiencing "very mild symptoms" and will continue to carry out all his duties, press secretary Karine Jean-Pierre said.
The president is taking the antiviral medicine Paxlovid, her statement added.
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In a tweet Mr Biden said he was "doing great" and "keeping busy".
His wife First Lady Jill Biden said she had tested negative.
Consistent with White House protocol the president will continue to work in isolation until he tests negative, Ms Jean-Pierre said - and will take part in meetings via telephone and Zoom.
White House Covid coordinator Dr Ashish Jha said the president was tired, with a runny nose and dry cough.
He said Mr Biden went to bed feeling fine but did not sleep well and then tested positive on Thursday morning.
Ms Jean-Pierre will hold a press briefing alongside Dr Jha at 14:00 ET (19:00 BST).
The White House medical unit will inform all close contacts of the president during the day, Ms Jean-Pierre said, including any members of Congress or members of the press who were with Mr Biden during his visit to Massachusetts on Wednesday.
First Lady Mrs Biden said she had spoken to her husband and he was "doing fine".
"He's feeling good. I tested negative this morning. I'm going to keep my schedule. According to CDC guidelines, I'm keeping masked," she said.
Mr Biden, who is the oldest president in US history and turns 80 this year, last tested negative for Covid on Tuesday, the White House said.
In a memo to Ms Jean-Pierre, Mr Biden's physician Kevin O'Connor said he thought the president would respond favourably due to being fully vaccinated and twice boosted, adding that the early use of Paxlovid provided "additional protection against severe disease".
Mr Biden was judged "fit for duty" and described as "healthy" and "vigorous" by Dr O'Connor during his last physical examination in November, according to the BBC's US partner CBS.
