Taoiseach Micheál Martin has tested positive for Covid-19 while in Washington for the St Patrick’s Day celebrations.
It was detected as part of Covid-19 screening required to enter the White House for a planned meeting with US President Joe Biden on St Patrick’s day.
The White House insists any person visiting must undergo tests for Covid-19.
It means he will be unable to meet Joe Biden in person later on Thursday as part of the traditional shamrock ceremony.
Mr Martin had been due to speak at the 30th anniversary of the Ireland Funds Gala dinner.
The speaker of the House of Representatives Nancy Pelosi was about to make an award to the Taoiseach, however it was instead Irish Ambassador Dan Mulhall who stepped onto the stage, and announced the Taoiseach had tested positive.
Officials said the meeting scheduled for the Oval Office on Thursday morning would almost certainly be cancelled.
The meeting may take place virtually, officials said.