KABUL, Afghanistan - U.S. and British forces have been accused by Afghanistan's government of running prisons where inmates are detained without trial.
A report presented to Afghan President Hamid Karzai alleged there were three detention centers in Kandahar Airfield and three others in Helmand province.
Karzai demanded an explanation from the U.S. and British governments.
"Foreign forces do not have the right to operate any detention facilities or imprison any Afghan within Afghanistan," Karzai said in a statement on Tuesday.
He called the "secret prisons" a "violation of Afghanistan’s sovereignty" and added that it was "a clear violation of the law of Afghanistan."
Abdul Shukoor Dadras, a member of the Afghan Commission for Prisoner Evaluation that presented the report, told NBC News on Wednesday that four of the sites were run by U.S. forces while two others were run by British forces.
According to Dadras, 28 Afghans were found detained at the Western bases. He said most of them had not been through any kind of legal proceedings.
Rear Admiral John Kirby, the Pentagon's press secretary, declined to comment about the allegations when asked about Karzai's statement at a briefing on Tuesday.
But U.S. defense officials told NBC News the facilities mentioned in the report were mainly used as temporary detention facilities for suspected terrorists or criminals before their formal transfer to Afghan authorities.
In a statement to NBC News, Britain's defense ministry said that all "detainees are held at the request of the Afghan authorities where there is evidence linking them to criminal activity."
Karzai has been Afghanistan's only president since U.S.-led forces toppled the Taliban regime in 2001. A general election was held earlier this month to find his successor, with a run-off between former Foreign Minister Abdullah Abdullah and and ex-Finance Minister Ashraf Ghani Ahmadzai looking likely.
The preliminary results are due to be finalized on May 14, after an investigation into fraud complaints.
Karzai's strong words are the latest flare-up in relations with the U.S.
He has refused to sign a security agreement allowing some U.S. troops to stay in the country beyond 2014, and his government announced in January it was to release inmates from Bagram detention center whom the U.S. said were "dangerous insurgents" with "blood on their hands."
Jim Miklaszewski and Courtney Kube of NBC News contributed to this report.