The US Justice Department has blocked the release of a Cuban-born exile wanted by Venezuela and Cuba in connection with a plane bombing.
Venezuela wants to try Mr Posada for a 1976 plane bombing
The department opposed a court ruling that anti-Castro activist Luis Posada Carriles should be freed from a Texas detention centre pending deportation.
A department spokeswoman said he might abscond and pose a security risk.
The Cuban plane exploded over Barbados in 1976, killing all 73 people on board - including Cuba's entire fencing team.
The bombing occurred exactly 30 years ago and Cuba is holding a remembrance ceremony on Friday.
Mr Posada - a former CIA operative - is being held in the US for crossing illegally from Mexico after serving time in Panama for plotting to kill Cuban President Fidel Castro.
He faces deportation, but it cannot be to Cuba or Venezuela because of fears he might face torture.
No other country has been willing to accept him.
Venezuela wants to try Mr Posada - who was born in Cuba but has Venezuelan citizenship - in connection with the bombing of the plane, which was flying to Cuba from Caracas.
The BBC's Greg Morsbach in Caracas says the Venezuelan authorities are quietly satisfied that for time being the man on their wanted list is not being set free.
He escaped from a Venezuelan prison in 1985 while awaiting a trial on appeal.
Mr Posada, now 78, was later convicted in Panama of trying to kill Cuban leader Fidel Castro at a summit in the country in 2002.
Both Venezuela and Cuba have accused the US government of harbouring a man they regard as a terrorist.