An Iranian detainee refused to appear at a U.S. military review hearing Friday, the sixth prisoner in a week to boycott a process to determine whether hundreds of Guantanamo Bay (search) prisoners are being properly held or should be set free.

The 25-year-old man, who according to the U.S. military was a Taliban (search) fighter in Afghanistan, relayed his decision through an officer assigned as his "personal representative."

"He dropped out," said the officer, an Air Force lieutenant colonel whose identity was barred from being made public. "He said, 'I don't want to participate anymore."'

The officer said the Iranian did not give a reason.

The detainee has told the military he was a cook and driver and wasn't involved in combat. In his absence, the open tribunal hearing lasted only 13 minutes, followed by a closed session to discuss classified information.

Eleven cases have been heard since the review tribunals were convened at the U.S. military prison last week. The other detainees who refused to appear were three Yemenis, one Saudi and one Moroccan.

The military has given no reason for their absence, other than to say they have been generally uncooperative.

"If I were them, I would naturally assume that these so-called hearings are just another pretext for extracting information," said Clive Stafford-Smith, a human rights lawyer in New Orleans who has worked on the cases of dozens of detainees. "They've got enough sense to see that this is a sham."

Human rights groups say the process is grossly inadequate because detainees are not allowed lawyers, and argue that the three military officers who sit on each tribunal can't be considered impartial. The military says members of the review tribunals are neutral.

The tribunal process began last week to determine whether some 585 prisoners at the prison should continue to be held as "enemy combatants." The hearings are the first opportunity detainees have had to formally plead their cases since they began arriving at Guantanamo in January 2002.

The review panels have the power to recommend reversing assessments that detainees are "enemy combatants," a classification that gives them fewer legal protections than prisoner-of-war status. The panels could also recommend freeing the prisoners. The initial decisions have yet to be announced but could come next week.

The military said the Iranian detainee, who has been held for more than two years, told investigators he traveled to Afghanistan to buy stereo parts and was conscripted by the Taliban.

The military said he was trained at a Taliban camp to use an AK-47 assault rifle that he used in combat.

"Although he might not have wanted to be a member of the Taliban, he was for about two months until he was caught by the Northern Alliance," a Marine officer assigned as tribunal recorder told the panel.

The Iranian has told military officials he surrendered.

Two Afghan detainees pleaded for their freedom Thursday in the first hearings observed by journalists. Both argued they happened to be with Taliban forces but never fought against American troops.

The review panels are separate from military commissions that are to try an initial group of four detainees on war crimes conspiracy and other charges. Pretrial hearings for those cases are planned later this month.

The military convened the Combatant Status Review Tribunals (search) in response to a Supreme Court (search) ruling in June that prisoners have a right to challenge their detention in U.S. courts.