Why is this man not a terrorist?

EL PASO, Texas (Reuters) - An anti-Fidel Castro militant accused of bombing a Cuban airliner in 1976 will remain detained on immigration charges after U.S. Justice Department lawyers on Thursday filed objections to a magistrate's recommendation that he be freed.

The lawyers called Luis Posada Carriles, 79, "an unrepentant criminal and admitted mastermind of terrorist plots and attacks on tourist sites."

But the government has stopped short of formally declaring him a terrorist, which would allow indefinite detention under post-September 11 anti-terrorism laws.

Posada's case has become a political problem for the U.S. administration because Cuba and Venezuela have declared him a terrorist for his suspected involvement in the bombing of the airliner en route to Cuba from Barbados in which 73 people were killed. They accuse the United States -- a long-time foe of Castro -- of a double standard in the war on terrorism.

Many Cuban-Americans consider him a "freedom fighter" against Castro's communist rule and they are an important U.S. voting bloc.

The U.S. government had until Thursday to respond to Magistrate Norbert Garney's finding last month that Posada, a naturalized Venezuelan originally from Cuba, must be released because time long ago expired for deporting him.

Posada has been held since May 2005 for illegally crossing the border from Mexico into Texas. Seven nations have refused U.S. requests to accept him. He argues he faces torture or worse if sent to Cuba or Venezuela.

Shortly after the filing of objections, U.S. Immigration and Customs Enforcement officials informed Posada by letter that he will be held pending further consideration of his case.

"You remain a flight risk, danger to the community, and danger to the national security," the ICE letter said. "Your case may have serious adverse foreign policy consequences for the United States."

Posada's lawyer planned to file a response on Friday.

The former CIA operative, who trained with other Cuban exiles for the U.S.-sponsored "Bay of Pigs" invasion to overthrow Castro in 1961, is fighting his detention on the ground that U.S. laws require officials to release him within 90 days if they cannot find a safe place to deport him.

The time limit has been extended at the government's request to allow further court consideration.

Posada, who has been ill, has publicly renounced violence against Castro and has said all he wants is to go to Miami to live with his family.