The US envoy for Venezuela, Elliott Abrams, has called the disappearance of a Venezuelan former intelligence chief from Spain "embarrassing".
Hugo Carvajal disappeared after a court in Spain ruled he should be extradited to the US, where he is accused of drug trafficking.
Spanish police have not been able to locate him in since Friday.
Mr Carvajal has in the past said that he does not trust the US justice system.
Who is Hugo Carvajal?
Gen Carvajal, 59, was the head of military counter-intelligence from July 2004 until December 2011, when Hugo Chávez was president of Venezuela.
In 2011, US prosecutors accused him of personally co-ordinating a US-bound shipment of more than five tonnes of cocaine from Venezuela to Mexico.
The indictment also accused him of being on the payroll of a Colombian drug lord and having links to Colombia's Marxist Farc rebels. He has repeatedly denied having any links to drug traffickers or the Farc, and says the charges are politically motivated.
In 2014, he spent three months in Aruba as Venezuela's consul general on the Dutch Caribbean island. During that time, he was detained by the authorities there at the request of the US state department.
But a judge on the island ruled that his arrest was illegal because the general held a diplomatic passport. He was released and was given a hero's welcome by Venezuelan President Nicolás Maduro in Caracas.
After another spell as military counter-intelligence chief, he became a politician for the governing socialist party and was elected to the National Assembly in 2016.
But in February 2019, Gen Carvajal turned against the government of President Maduro and backed opposition leader Juan Guaidó as Venezuela's leader.
He also urged the military to switch sides, which prompted the Venezuelan government to strip him of his rank. He fled Venezuela on a boat to the Dominican Republic and on to Spain, where he was arrested in April at the request of US authorities.
Prosecutors appealed against the ruling and on Friday, Spain's highest court overturned the lower court's decision.
But when police went to Mr Carvajal's home to detain him, he was not there. Spanish police have confirmed that they are searching for him.
His lawyer told the New York Times that she did not know where her client was.
What has the reaction been?
The US envoy for Venezuela mocked the Spanish authorities.
"They went to his home and, what a surprise, he wasn't there," Mr Abrams told reporters.
"Carvajal's disappearance is quite embarrassing for the Spanish government," he added.
The US authorities have in the past said they believe Mr Carvajal holds incriminating information on President Maduro.
The US and the government of President Maduro have been at loggerheads for years, with the former imposing tough sanctions on the latter.