Venezuela's President Nicolas Maduro is expelling three US consular officials, accusing them of meeting students involved in anti-government protests.
The country has seen growing political tension and rallies, with three protesters dying in clashes last week.
An arrest warrant has been issued for opposition leader Leopoldo Lopez, who has pledged to lead a march in the capital Caracas on Tuesday.
The US has expressed concern about arrests of opposition protesters.
Maduro did not name the US officials being expelled, when he made the announcement in a national TV broadcast, but said the foreign ministry would give details later.
"It's a group of US functionaries who are in the universities. We've been watching them having meetings in the private universities for two months. They work in visas," the president said.
On Saturday, US Secretary of State John Kerry issued a statement expressing concern about the rising tensions in Venezuela.
"We are particularly alarmed by reports that the Venezuelan government has arrested or detained scores of anti-government protestors and issued an arrest warrant for opposition leader Leopoldo Lopez," read the statement.
The main opposition grievances are high inflation, crime and the shortage of some staples.
The government has blamed the shortages on "saboteurs" and "profit-hungry corrupt businessmen".
Opposition leader Leopoldo Lopez was last seen on Wednesday, when three men were shot dead at the end of opposition protests in the capital.
In a video posted online on Sunday, Lopez says he has not committed any crime and challenges the authorities to arrest him during the Tuesday march.
President Nicolas Maduro says an arrest warrant was issued against Lopez shortly after the incidents.
Maduro has accused Lopez of inciting violence as part of a coup plot against his left-wing government.
The opposition say they were killed by pro-government militias known as "colectivos".
Lopez, 42, is a former mayor of Chacao district, in eastern Caracas. He organised the recent protests against the government.
On Sunday morning, Venezuelan police searched the houses of Lopez and his parents.
Hours later, he posted a new message on Twitter and a three-minute long video.
"I want to invite all of you to join me on a march on Thursday, from Venezuela Square [in central Caracas] towards the Justice Ministry building, which has become a symbol of repression, torture and lies," Lopez said on the video.
He called on his supporters to dress white, "to reaffirm our commitment to peace".
"I will be there to show my face. I have nothing to fear. I have not committed any crime. If there is any order to illegally arrest me, well, I will be there," added Lopez.