Nearly 30 per cent of the detainees at the US base in Guantanamo Bay in Cuba have been cleared to leave the prison.
However, the 141 men remain jailed because the US government has been unable to arrange for their return to their home countries, the Pentagon said today.
The Pentagon refused to identify the men despite having released its first comprehensive list of detainees held at the prison earlier this week.
Of these 141 detainees among the 490 still at Guantanamo, various military reviews have cleared 22 to be freed in their home countries and the remaining 119 for transfer to the control of their home governments.
"It's just an outrageous situation where people have gone through this system that has been established, such as it is, and the (US) government itself has found there's no reason for them to be held any longer, and yet they continue to be held," said Curt Goering, a senior Amnesty International USA official.
"It makes a mockery of any kind of system of justice," he added.
Defence officials said the United States has no interest in detaining anyone for any longer than necessary and has been able to arrange for some detainees, but not others, to return to their home countries.
Officials cited US policy not to expel, return or extradite individuals to other countries where it is more likely than not that they will be tortured or persecuted.
Rights activists decry the indefinite detention of Guantanamo detainees since the jail opened in January 2002, and accuse the United States of torture. The Pentagon denies the torture allegations and says many dangerous al-Qaeda and Taliban figures are held there.
The detainees hail from 40 countries and the West Bank, with the largest number from Saudi Arabia, followed by Afghanistan and Yemen.