Venezuelan President Hugo Chavez says he is expelling a US official accused of spying with Venezuelan officers.
Hugo Chavez has said any US spies will be arrested
The naval attache at the US embassy, John Correa, would be forced to "leave immediately", Mr Chavez said in a speech to mark seven years in power.
US officials said the charges were baseless and Captain Correa had left for medical treatment and a holiday.
Mr Chavez has repeatedly accused the US of supporting attempts to overthrow him, a charge Washington denies.
Ties between Venezuela's left-wing government and Washington have been strained for several years, but it is the first time Venezuela has decided to expel a US official.
In Washington, US Defence Secretary Donald Rumsfeld described the election of a string of left-wing leaders in the region as worrying.
"[Chavez] is a person who was elected legally, just as Adolf Hitler was elected legally and then consolidated power," he said.
"Now [Chavez] is of course working closely with [Cuban President] Fidel Castro and [Bolivian President Evo] Morales and others.
"It concerns me."
Thursday's announcement came three days after Mr Chavez said agents had infiltrated an alleged spy ring at the US embassy.
"We have decided... to throw out of the country a military official from the mission of the United States for espionage," the president said.
He warned that the full US embassy military mission would be expelled if authorities caught any of its officers spying.
"The next step would be to withdraw the whole so-called military mission of the United States," Mr Chavez said.
He had threatened last week to have any American officials involved in spying arrested.
In the past week, Venezuela has also said that several of its military officers have been caught passing state secrets to the US.
Relations between the US and Venezuela were already under strain before the spying row erupted.
Washington is deeply opposed to the government of left-wing Mr Chavez, who is a vocal critic of the US.
The US has expressed concerns about Venezuelan democracy under Mr Chavez and about the effect of his government's military purchases on regional stability.
The US has tried to block his attempts to buy military equipment using American technology.