Venezuelan President Nicolás Maduro has broken off relations with the US after it recognised opposition leader Juan Guaidó as interim leader.
Mr Maduro gave US diplomats 72 hours to leave the country but the US said the “former president” no longer had the authority to order them out.
On Wednesday, Mr Guaidó had declared himself president during mass protests.
The US has urged the military to back Mr Guaidó, but so far it has remained loyal to Mr Maduro.
Mr Maduro took office in 2013 after the death of Hugo Chávez. He was sworn in for a second term this month after elections last May that were marred by an opposition boycott and widespread claims of vote-rigging.
Venezuela has been in economic freefall. Hyperinflation, power cuts and shortages of basic items have driven millions of people from the country.
President Donald Trump recognised Mr Guaidó as interim president in an apparently co-ordinated move minutes after the 35-year-old declared himself acting leader.
In a statement, he described Mr Maduro’s leadership as “illegitimate”, adding: “The people of Venezuela have courageously spoken out against Maduro and his regime and demanded freedom and the rule of law.”
It warned Mr Maduro tougher sanctions could be imposed.
Mr Trump told journalists he was not considering military action but added that “all options are on the table”.
He called on other nations to follow suit in supporting Mr Guaidó.