Afghan investigators have accused the American military of abusing detainees at its main prison in the country, bolstering calls by President Hamid Karzai for the U.S. to turn over control of the facility and complicating talks about America's future role in Afghanistan.

The investigators also called on Saturday for any detainee held without evidence to be freed, putting the U.S. and Afghan governments on a collision course in an issue that will decide the fate of hundreds of suspected Taliban and al-Qaeda operatives captured by American forces and held indefinitely.

Karzai took Washington by surprise Thursday when he ordered that the U.S. military turn over full control of the prison outside Bagram Airbase within one month, a seemingly impossible deadline given U.S. security concerns about the prisoners and the Afghan government's weak administrative capacity. The countries had been working on phasing a transfer of responsibility of the prison, which holds 3,000 detainees, over two years.

The demand was the latest episode of political brinkmanship as negotiations continued for a Strategic Partnership Document with America that will determine the U.S. role in Afghanistan after 2014, when most foreign troops are due to withdraw. Karzai has demanded an end to unpopular night raids by U.S. troops and control over detainees as a condition of the pact and could be seeking leverage by pushing the detainee issue now.

Karzai spokesman Mohammad Sediq Amerkhil said Saturday that the president's remarks were a direct response to the investigation team's report of abuse and prolonged detentions.

The charges are reminiscent of allegations surrounding the U.S. treatment of detainees at Guantanamo Bay, Cuba, where admitted Sept. 11 mastermind Khalid Sheikh Mohammed is held.

Complaints over conditions

Detainees interviewed during two visits to the U.S.-run portion of the Parwan detention centre outside Bagram Airbase — about 40 kilometres north of Kabul — complained of freezing cold, humiliating strip searches and being deprived of light, according to Gul Rahman Qazi, who led the investigation ordered by Karzai.

Another investigator, Sayed Noorullah, said the prison and all detainees must be transferred to Afghan control "as soon as possible," adding, "if there is no evidence ... they have the right to be freed."

U.S. Embassy spokesman Gavin Sundwall said Saturday that American officials only recently received the commission's report. He said the U.S. investigates all allegations of prisoner abuse.

"We will certainly take seriously the report and study it," he said. He added that the U.S. is committed to working with the Afghan government on a joint plan to turn over detainees "in a responsible manner." He would not specify what time frame would be considered responsible.

Karzai's recent relationship with the U.S. has been rocky, even though he came to power after the 2001 American-led intervention to drive the Taliban regime from power for sheltering al-Qaeda. He has frequently lashed out at Washington, although he needs U.S. military and financial strength to back his weak government as it battles the Taliban.

Last year, he accused the U.S. and its allies of serving only their own purposes in the country, and has told a Pakistani television station he would support Pakistan in any war against the United States. In 2010, he was said to have threatened to join the Taliban if foreign donors pressured him too much.

The rhetoric is seen as a play for support from an Afghan population that resents the U.S. presence and is angered by reports of Afghans detained indefinitely and of residents whose homes are invaded without warning. Less clear is exactly what Karzai hopes to gain from Washington with the politics of confrontation.