WASHINGTON, July 19 (Reuters) — President Joe Biden's administration said on Monday that it had transferred its first detainee from the U.S. military prison at Guantanamo Bay, a Moroccan man who had been imprisoned since 2002, bringing the population at the facility down to 39.

Set up to house foreign suspects following the Sept. 11, 2001, attacks on New York and Washington, the prison came to symbolize the excesses of the U.S. “war on terror” because of harsh interrogation methods that critics say amounted to torture.

While Trump kept the prison open during his four years in the White House, Biden has vowed to close it.

Abdul Latif Nasir, who is 56 years old, was repatriated to Morocco. He had been cleared for release in 2016.

"The (Biden) administration is dedicated to following a deliberate and thorough process focused on responsibly reducing the detainee population of the Guantanamo facility while also safeguarding the security of the United States and its allies," State Department spokesman Ned Price said in a statement.

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Most of the prisoners left at Guantanamo Bay have been held for nearly two decades without being charged or tried.

Opened under President George W. Bush, the prison’s population grew to a peak of about 800 inmates before it started to shrink. President Barack Obama whittled down the number further, but his effort to close the prison was stymied largely by Republican opposition in Congress.

The federal government is still barred by law from transferring any inmates to prisons on the U.S. mainland. Even with his own Democratic party now controlling Congress, Biden has majorities so slim that he would face a tough challenge securing legislative changes because some Democrats might also oppose them.

U.S. Secretary of State Antony Blinken said last month that the administration is "actively looking" into recreating the position of a State Department envoy for the closure of the prison at the Guantanamo Bay naval base.

(Reporting by Idrees Ali Editing by Gareth Jones and Steve Orlofsky)