The United States on Thursday expanded its probe of alleged prison abuses to include all Iraqi-run detention sites, saying the Shiite-led government had agreed to the move after U.S. forces uncovered a secret Interior Ministry chamber in Baghdad where Sunni Arabs allegedly were tortured and starved.

Early Friday, two large bombs exploded just outside that Interior Ministry facility, knocking down concrete barriers, collapsing nearby buildings and leaving a huge crater in the street. Rescue workers, surrounded by burning vehicles and bloodied people, were climbing over the wreckage in search of trapped victims and pulling women and children from the debris. There was no immediate word about casualties.

Law enforcement officials from the FBI, Justice Department, U.S. Embassy and U.S.-led military forces will aid an Iraqi-appointed citizens group in the prison investigation, slated to cover all of at least 1,100 sites across the country where Iraqi security forces and justice officials are holding detainees.

The breadth of the crackdown -- and involvement by top U.S. officials including Army Gen. George Casey, Ambassador Zalmay Khalilzad and others -- indicated the gravity with which American leaders here viewed the torture allegations and the scandal's possible impact on the already marginalized Sunni community, whose support is vital to ending the insurgency.

Iraqi and U.S. officials agreed on a six-point plan intended to "ensure humane treatment of all detainees," the embassy said in a statement. U.S. diplomats also issued a rare public rebuke to the U.S.-supported government, warning the administration about growing charges that it was letting former Shiite factional militias run the country's police forces.

"We have made clear to the Iraqi government that there must not be militia or sectarian control or direction of Iraqi security forces, facilities, or ministries," the embassy statement said.

The tough talk between allies follows the discovery last weekend of scores of detainees -- most apparently Sunnis and many of them held for months -- in a former bomb shelter of an Interior Ministry building. The captives were found Sunday by soldiers from the U.S. Army's 3rd Infantry Division.

Prime Minister Ibrahim Jafari, after meetings with the top U.S. military and diplomatic leaders in Iraq, publicly revealed details of the U.S. raid on Tuesday. Jafari, the leader of one of Iraq's most prominent Shiite religious parties, said he had been told some of the men appeared malnourished and had been tortured.

Sunni Arab leaders and Sunnis who said they had been held in the bunker gave accounts of bloody beatings, torture with electric shock and, in one case, being suspended from the ceiling in chains. An American television journalist saw emaciated men being taken from the center, and Maj. Gen. Hussein Kamal, a top Interior Minister official, said the skin of some detainees had been stripped off.

On Thursday, Interior Minister Bayan Jabr, a Shiite who directs roughly 100,000 police and special police officers, denied the allegations of widespread torture at the secret prison and broader allegations of Shiite militia and Iranian involvement in the ministry's forces.

Jabr said a U.S. general who discovered the underground prison had told him of finding five or six victims of beatings or other abuses. Allegations of more widespread mistreatment at the center, Jabr insisted, were "untrue and inaccurate."

"I reject torture, and anyone found guilty of that will be punished," he said.

Jabr told reporters that the detention center had been opened by Iraq's previous government and that he had kept it open only because the country lacked adequate prisons. When he took office, he said, the hidden prison was used as an Interior Ministry investigation facility.

At a news conference, Jabr waved a sheaf of what appeared to be passports. "Those who were held inside the center were some of the most dangerous criminal terrorists of various Arab nationalities," he declared. "Let me tell you, those who were inside the shelter house were Arab killers, and here are their passports, IDs. They are Arabs and some of the most dangerous terrorists."

Among the reported 173 detainees was an Iraqi Shiite, crippled by polio, who had taken $1,000 from insurgents to detonate car bombs and booby traps that killed more than 60 Iraqis, Jabr said.

Jabr said that while U.S. generals found what they said were cases of torture, Casey, the commander of U.S. forces in Iraq, also told him that "all the suspects' files were in order -- which shows that our practices and procedures are correct." All the men at the center were there on a judge's orders, Jabr said.

U.S. military investigators, however, said troops had discovered 168 detainees and files for only 116 of them.

Scandal over the secret prison has forced the seven-month-old Shiite-led government to confront growing charges of mass illegal detentions, torture and killings of Sunni men. Members of the Sunni minority, locked in a struggle with the Shiite majority over the division of power in Iraq, say men dressed in Interior Ministry uniforms have repeatedly rounded up Sunni men from neighborhoods and towns. Bodies of scores of them have been found dumped by roadsides or in gullies.

Most of the allegations have been directed at the Badr Organization, the former armed wing of the Supreme Council for the Islamic Revolution in Iraq, a Shiite party that was founded in exile in Iran and is now the leading party in Iraq's government.

Some Iraqi Sunnis involved in the insurgency have said the sweeps by the Shiite-controlled security forces are putting more pressure on their groups than U.S. military raids and are one of the factors driving the Sunni resistance to try shifting -- at least temporarily -- from guerrilla warfare to politics.

The airing of the allegations may widen Iraq's sectarian rifts if Sunnis believe the government and the Americans are not trying to correct abuses. U.S. officers, however, maintain the American raid on the secret prison already has won back some Sunni confidence in U.S. efforts here.

Army Lt. Gen. Martin Dempsey, who oversees training of Iraq's security forces, said the prison case "points out the necessity for an internal oversight that clearly isn't there" for everyone taken into custody by Iraq's security and intelligence services.

"These kinds of things are a huge detriment to the morale of the force," Dempsey said. "I think the ministry understands it, or I hope it does. We're looking for them to take it seriously."

Iraqis pray in Baghdad in front of the coffin of Yasir Salah, 70, who relatives say died in detention after being arrested Sunday by Interior Ministry special forces.