Five detainees at the US naval base in Guantanamo, Cuba, have refused to participate in military hearings to review their cases, officials say.
Nearly 600 inmates remain in Guantanamo
They are among eight men - including an Algerian, three Yemenis, a Moroccan and a Saudi - whose cases have come up before a new military panel.
The tribunals' recommendations are not yet known.
They are due to decide whether prisoners should continue to be detained as enemy combatants or freed.
The reviews were set up after the US Supreme Court ruled the detainees had a right to challenge their detentions.
All of the detainees will eventually go through the process, the US authorities say.
The detainees who refused to appear when called this week were the Saudi, the Moroccan and three Yemenis. Their names have not been released.
They had "historically not co-operated", defence department spokeswoman Commander Beci Brenton said.
"While they have been here, they have not cooperated with interrogators," she added.
According to the spokeswoman, of the four who had refused to co-operate:
- one Yemeni admitted being with Osama bin Laden during the siege of the Tora Bora caves near the Afghanistan-Pakistan border in 2001 and was "captured with an AK-47 rifle"
the Saudi, 29, fought on the front line in Afghanistan and was later captured in Pakistan
the Moroccan, 32, was a Taleban fighter captured by the Northern Alliance in Afghanistan
The first detainee who was reviewed, a 24-year-old Algerian, reportedly said he would "kill Americans" if released.
The BBC's Nick Childs in Guantanamo says the number of detainees refusing to appear could make it problematic for the military to argue that the tribunals are a valid process.
However, US Navy Secretary Gordon England, who is observing the hearings, said the process was fair and in accordance with international law.
"Prisoners of war are determined to be prisoners of war by the Geneva Convention Article five," he said.
"These detainees are not prisoners of war, they're not part of a country that declared war on the United States, they do not follow the Geneva Convention, as a matter of fact they do exactly the opposite of what the Geneva Convention asks," he added.
US officials say all the prisoners reviewed so far received some form of military training in Afghanistan and also had some sort of association with the Taleban and al-Qaeda.
A number had reportedly also admitted to fighting against the US-led forces.
Critics have dismissed the tribunals as inadequate, not least because the detainees do not have access to a lawyer.
The Pentagon insists that they are fair and it is allowing a small group of journalists to observe some of them in action, although not any of the classified intelligence against the detainees.