KABUL, Afghanistan — A commission appointed by President Hamid Karzai to investigate detention facilities run by American and British forces in southern Afghanistan claimed Saturday to have uncovered secret prisons on two coalition bases, an allegation that could not be immediately confirmed but that was likely to further complicate relations between the Afghan government and its allies.

“We have conducted a thorough investigation and search of Kandahar Airfield and Camp Bastion and found several illegal and unlawful detention facilities run and operated by foreign military forces,” said Abdul Shakur Dadras, the panel’s chairman.

Mr. Dadras offered no evidence to support his assertion, though he promised to release more details after presenting his report to Mr. Karzai.

Lt. Col. J. Todd Breasseale, a spokesman for the Defense Department, wrote in an email, “Every facility that we use for detention is well known not only by the government of the Islamic Republic of Afghanistan, but also by the I.C.R.C.,” a reference to the International Committee of the Red Cross, a nonpartisan organization that provides humanitarian care for victims of conflict.