SAN JUAN, Puerto Rico -- The U.S. began a series of secret hearings Friday to determine whether 14 alleged terrorist leaders at its prison in Guantanamo Bay, Cuba, should be declared "enemy combatants" who can be held indefinitely and prosecuted by military tribunals.

No details were released and a military spokesman, Navy Cmdr. Chito Peppler, declined to identify detainees who appeared before the panel of three officers.

Edited transcripts of the hearings at the U.S. Navy base in southeast Cuba will be released later, Peppler said.

The 14 detainees, including an alleged mastermind of the Sept. 11, 2001, attacks, were moved in September from a secret CIA prison network to the prison at Guantanamo Bay, where the U.S. holds about 385 men on suspicion of links to al-Qaida or the Taliban.

Some are expected to boycott the proceedings and their hearings will be held in absentia, Peppler said.

The military held 558 combatant status review tribunals between July 2004 and March 2005 and the panels concluded that all but 38 detainees were "enemy combatants" who should be held. Those 38 were eventually released from Guantanamo.

The military allowed the media to cover previous hearings but this time has adopted more stringent rules, barring anyone without a special security clearance. The 14 detainees include Khalid Sheikh Mohammed, a suspected mastermind of the Sept. 11 attacks who was captured in Pakistan in March 2003, and other alleged al-Qaida figures.

Bryan Whitman, a Pentagon spokesman, said Mohammed was not among those who appeared before the panel Friday.

Legal experts have criticized the U.S. decision to bar independent observers from the hearings and The Associated Press filed a letter of protest, arguing that it would be "an unconstitutional mistake to close the proceedings in their entirety."

Meanwhile, the U.S. government has agreed to free Abdullah bin Omar, a Tunisian being held at Guantanamo, an official for a London-based group working on behalf of prisoners said Friday.

The Tunisian is among about 80 detainees who have been cleared for release or transfer from the Guantanamo Bay prison by a U.S. military review panel, said Christopher Chang, an official with the group Reprieve.

Bin Omar is one of 12 Tunisian citizens held in Guantanamo, according to documents released by U.S. authorities. Reprieve represents four of them, including bin Omar.