Pentagon officials have confirmed that Guantanamo detainees may still be kept in detention, even if they are found not guilty by a military tribunal.
Hundreds of terror suspects are held at Guantanamo Bay in Cuba
They say detainees could be kept prisoner if they are considered a security risk.
If found guilty, they could also be held beyond any sentence laid down by the tribunal.
The Pentagon this week laid the first charges against two foreign detainees held in Guantanamo Bay.
'Not common sense'
US military officials argue that there are two processes under way, BBC Pentagon correspondent Nick Childs says .
Detainees are being held because they are suspected of being enemy combatants in an ongoing war.
Separately, some may be put before tribunals accused of specific war crimes or other offences.
But the officials say it would not be common sense to release detainees after trials if it was thought they might launch new attacks on US interests.
The officials add that anyone convicted of war crimes would have to serve out their sentences - even if other detainees were released because the war on terrorism was deemed to be over.
The trial process has been widely criticised by human rights groups.
They say there is a lack of right to appeal, a lack of independence, and the defendants' rights to choose their own counsel and mount an effective defence will be restricted.
A lawyer appointed by the US military to represent one of the first detainees at Guantanamo Bay to be charged has also voiced his concerned.
"The tribunals don't have the safeguards that one would expect," he told the BBC's World Today programme.
"This is unlike any system we have seen since at least World War II - except perhaps similar military commissions in other countries that we frequently criticise as fundamentally unfair," he said.