Biden tested negative on Tuesday, she said.

Psaki tweeted that she took a laboratory test for Covid-19 in preparation for the trip, which gets underway on Wednesday, and was later notified of a positive result.

She said she had two “socially distanced meetings” with Biden on Monday and that he is not considered a “close contact” under guidelines from the Centers for Disease Control and Prevention.

She said she shared the news “out of an abundance of transparency”.

Psaki tweeted and released a statement a short time before she was scheduled to step into the White House press room for her daily briefing, accompanied by National Security Adviser Jake Sullivan, who was joining her to discuss the trip.

After a brief delay, Chris Meagher, a deputy press secretary, introduced Sullivan to a waiting White House press corps and he proceeded with the briefing.

Psaki said she will follow CDC guidance and no longer accompany Biden on his stops in Belgium, for a series of meetings with European leaders on Russia’s war in Ukraine, and in Poland, which shares a border with Ukraine and has taken in millions of Ukrainians fleeing warfare.

Psaki said she has only experienced mild symptoms and credited being vaccinated against Covid-19.

She said under White House Covid-19 protocols, she will work from home and plan to return to work at the end of a five-day isolation period and a negative test.

This is the second time that Covid-19 has forced Psaki to bow out of accompanying Biden abroad.

She sat out last autumn’s trip to Rome and Glasgow after disclosing she had tested positive.