WASHINGTON - US President Joe Biden tested positive for COVID-19 on Wednesday, the White House confirmed.

"Earlier today following his first event in Las Vegas, President Biden tested positive for COVID-19. He is vaccinated and boosted, and he is experiencing mild symptoms," White House Press Secretary Karine Jean-Pierre said in a statement.

"He will be returning to Delaware where he will self-isolate and will continue to carry out all of his duties fully during that time," she said.

"The president presented this afternoon with upper respiratory symptoms, to include rhinorhea (runny nose) and non-productive cough, with general mailaise," according to a note from Biden's doctor provided by Jean-Pierre.

Biden was scheduled to speak at a conference for the Latino civil rights and advocacy group UnidosUS, but he would no longer be able to attend.

"Regrettably, I was just on the phone with President Biden and he shared his deep disappointment at not being able to join us this afternoon. The president has been at many events, as we all know, and he just tested positive for Covid," Janet Murguia, president of the group, told attendees after Biden was late to his scheduled appearance.

This is not the first time the 81-year-old Biden tests positive for COVID-19. He previously tested positive in 2022.

The latest news came as Biden faces mounting pressure from some Democrats to step down from the presidential race due to concerns about his age and mental fitness following his poor debate performance against former US president Donald Trump in late June.