A Cuban militant accused of masterminding the 1976 bombing of a Cuban airliner will remain in U.S. immigration custody for the foreseeable future, but efforts to deport him to a country willing to accept him will continue, officials say.

Luis Posada Carriles was arrested in Miami in May after illegally entering the United States through Mexico. He is being held by U.S. Immigration and Customs Enforcement in El Paso, Texas.

ICE issued a statement saying that Posada will not be released from its custody "at this time" and that further review was needed to determine where he could be sent.

A federal immigration judge ruled last fall that Posada could not be deported to Cuba or Venezuela, citing the possibility he could be tortured.

That prohibition, according to the ICE statement, "does not impede ICE from removing Mr. Posada to a third country."

Posada's attorney in Miami, Eduardo Soto, said the agency's decision appears to be an attempt to keep Posada in custody indefinitely without just cause and that he plans to ask a federal court to free him.

"Obviously, this is going to come to a head very quickly here," Soto said. "They've got to show some likelihood that he is going to a third country or they have to release him."

His lawyers have said they want assurances that any third country would not then send him to Cuba or Venezuela.

Posada, a former CIA operative and a fervent foe of Cuban President Fidel Castro, is accused by Cuba and Venezuela of plotting the 1976 bombing while living in Venezuela. He has denied involvement in the bombing, which killed 73 people.

Posada escaped from a Venezuelan prison in 1985 while awaiting retrial on the airline bombing charges, and Venezuela has formally sought his extradition. He also has been linked to a series of 1997 bombings in Cuba, one of which killed an Italian tourist.

In 2004, Posada and three others were pardoned by Panama's president for their alleged roles in a plot to assassinate Castro during a conference in Panama in 2000. Some Cuban-Americans consider him a freedom fighter.

Meanwhile, a federal judge has ordered the U.S. Marshals Service to deliver Posada to Fort Lauderdale for the May trial of one of his close associates. Santiago Alvarez faces federal weapons charges involving a cache of machine guns, a grenade launcher, explosives and silencers.