Only one in 10 of the prisoners held at the US prison camp at Bagram airbase have been charged and many are being abused and tortured, Afghan investigators revealed on Saturday.
Gul Rahman Qazi of the government's constitution watchdog said that just 300 of the 3,000 detainees had legal cases against them and Nato forces don't have enough evidence against the rest.
Inmates say they are kept in dark, freezing cells and humiliated with body cavity searches.
Mr Qazi said one elderly man had been locked in a pitch-black room and lost a tooth when punched by a guard.
Fellow investigator Sayed Noorullah said: "If there is no evidence they have the right to be freed," and the Afghan government should take control of the prisoners "as soon as possible."
President Hamid Karzai ordered the creation of the Independent Commission for Overseeing the Implementation of the Constitution last Thursday after demanding the US hand over its prisons to Afghan officials by February.
"Foreign troops are not allowed to run prisons in Afghanistan, which is sovereign and has its own constitution," Mr Karzai said.
He accused US occupation forces of violating the Afghan constitution and international human rights laws.
The Taliban derided Mr Karzai's tough talk in a statement released on Friday.
"He speaks of national sovereignty and of the welfare of people but practically we see that there are thousands of Afghan detainees who have been suffering at Bagram and other American bases now for years and without a trial."
It claimed that Mr Karzai "relies on a limited number of warlords for continuing his reign rather than relying on the support of the nation."
A US embassy spokesman said it would investigate the abuse allegations.