For years, extremist Iraqi detainees in U.S. custody held self-styled Islamic courts and tortured or killed inmates who refused to join them, military officials said, disclosing new details about the use of American prisons to recruit for the insurgency.

The problem became the main catalyst for a decision to separate moderate detainees from the extremists, part of a broader reform package aimed at correcting widespread U.S. prison abuses that sparked international criticism.

"We were having people who weren't insurgents who were being forced to be insurgents because of the power of these courts, the power of al-Qaida and other extremist groups," said Lt. Col. Kenneth Plowman, a spokesman for Task Force 134, which operates coalition detention facilities in Iraq.

He told The Associated Press Friday that the jailhouse Sharia courts were formed, despite the presence of U.S guards, to enforce an extreme interpretation of Islamic law. They were then used to convict moderate inmates, who were then tortured or killed, he said.

In comments published in the Sierra Vista Herald in Arizona, Brig. Gen. Rodney L. Johnson, commander of the U.S. Army Criminal Investigation Command, put the number of detainees tried by the courts in the double-digits. Neither he nor Plowman would give specific numbers.