Fearing that courts might order the detainees' release, security forces obtained a court order and transferred them to Baghdad, where they were held in isolation. Human rights officials learned of the facility in March from family members searching for missing relatives. The revelation of the secret prison could worsen tensions at a highly sensitive moment in Iraq. As U.S. troops are withdrawing, Maliki, a Shiite Muslim, and other political officials are negotiating the formation of a new government. Including minority Sunni Arabs is considered by many to be key to preventing a return of widespread sectarian violence. Already there has been an increase in attacks by Al Qaeda in Iraq, a Sunni extremist group. The alleged brutal treatment of prisoners at the facility raised concerns that the country could drift back to its authoritarian past. Commanders initially resisted efforts to inspect the prison but relented and allowed visits by two teams of inspectors, including Human Rights Minister Wijdan Salim. Inspectors said they found that the 431 prisoners had been subjected to appalling conditions and quoted prisoners as saying that one of them, a former colonel in President Saddam Hussein’s army, had died in January as a result of torture. "More than 100 were tortured. There were a lot of marks on their bodies," said an Iraqi official familiar with the inspections. "They beat people, they used electricity. They suffocated them with plastic bags, and different methods." An internal U.S. Embassy report quotes Salim as saying that prisoners had told her they were handcuffed for three to four hours at a time in stress positions or sodomized. "One prisoner told her that he had been raped on a daily basis, another showed her his undergarments, which were entirely bloodstained," the memo reads. Some described guards extorting as much as $1,000 from prisoners who wanted to phone their families, the memo said. Maliki vowed to shut down the prison and ordered the arrest of the officers working there after Salim presented him with a report this month. Since then, 75 detainees have been freed and an additional 275 transferred to regular jails, Iraqi officials said. Maliki said in an interview that he had been unaware of the abuses. He said the prisoners had been sent to Baghdad because of concerns about corruption in Mosul. "The prime minister cannot be responsible for all the behavior of his soldiers and staff," said Salim, praising Maliki's willingness to root out abuses. Salim, a Chaldean Christian, ran for parliament in last month's elections on Maliki's Shiite-dominated list. Maliki defended his use of special prisons and an elite military force that answers only to him; his supporters say he has had no choice because of Iraq's precarious security situation. Maliki told The Times that he was committed to stamping out torture — which he blamed on his enemies. "Our reforms continue, and we have the Human Rights Ministry to monitor this," he said. "We will hold accountable anybody who was proven involved in such acts." But Maliki's critics say the network of special military units with their own investigative judges and interrogators are a threat to Iraq's fragile democracy. They question how Maliki could not have known what was going on at the facility, and say that regardless, he is responsible for what happened there. "The prison is Maliki's because it's not under the Ministry of Defense, the Ministry of Justice or Ministry of Interior officially," said one Iraqi security official, who spoke on condition of anonymity because of the sensitivity of the topic. The revelations echoed those at the beginning of Iraq's sectarian war. In late 2005, the U.S. military found a secret prison in an Interior Ministry bunker where Sunnis rounded up in police sweeps were held. The latest episode, the U.S. Embassy report warns, could exacerbate tensions between Iraq's Shiite majority and Sunnis even with the facility closed. U.S. troops already have pulled out of Iraq's cities, and Iraqi officials say U.S. influence is diminishing as the Americans focus on ending their military presence. The number of U.S. troops in Iraq is scheduled to drop by about half, to 50,000, by the end of August.