A U.S.-led raid uncovered an underground prison run by Iraq's Interior Ministry where detainees allegedly were being tortured, the prime minister said Tuesday. Separately, a Sunni Arab leader accused the government of involvement in the kidnapping and killing of 46 Sunni men.

The new accusations against the Shiite-dominated government's security forces came on a day when bombings and ambushes across the country killed 13 Iraqi policemen, authorities said.

The U.S. military reported that three Marines and 80 insurgents had been killed over the past 48 hours in western Iraq, where a U.S. offensive came up against more than 100 insurgent bombs and mines. In addition, the military said three soldiers were killed Tuesday by a roadside bomb northwest of Baghdad.

In Baghdad, Prime Minister Ibrahim Jafari and other officials told reporters that detainees had been found in a basement of an Interior Ministry complex in the heart of the capital.

"I was informed that there were 173 detainees held at an Interior Ministry prison and they appear to be malnourished. There is also some talk that they were subjected to some kind of torture," Jafari said.

U.S. and Iraqi forces discovered the inmates when they went into the compound suspecting that individuals there may have been mistreated, the Pentagon said.

The troops "found things that concerned them," said Bryan Whitman, a Pentagon spokesman. Whitman did not say when the inmates were found, but U.S. troops took control of the Interior Ministry building Sunday.

Talk of a secret detention center at the Interior Ministry compound had surfaced in Baghdad this summer. Officials of the ministry, whose ranks are made up mainly of former members of Shiite militias, have repeatedly acknowledged some human rights abuses by their forces but never confirmed the rumors of a secret torture center run with the help of intelligence agents from neighboring Iran.

The first official acknowledgment of the allegations came Monday, when Maj. Gen. Hussein Kamal, the Interior Ministry's undersecretary for security, said an investigation would be opened into unspecified reports that ministry officers tortured suspects detained in connection with the country's insurgency.

The Associated Press quoted the head of Iraq's largest Sunni political party as saying that all the detainees were members of Iraq's Sunni Arab minority, which dominated the country under Saddam Hussein. Sunnis now lead the insurgency against U.S. and Iraqi forces and the U.S.-backed government.

"In order to search for a terrorist, [Iraq's new security forces] used to detain hundreds of innocent people and torture them brutally," Mohsen Abdul Hamid, leader of the Iraqi Islamic Party, told the news agency. Government officials had dismissed his earlier complaints about such a torture center, Abdul Hamid told the AP.

Borrowing a term from recent Latin American political history, Sunni leaders have accused Jafari's government of waging a "dirty war" of disappearances and killings targeting Sunni men since his administration came to power in April.

On Tuesday, Col. Abdulhadi Hussein of the Interior Ministry police confirmed the discovery of 28 bodies at the town of Jassan, near the Iranian border. When police found the men Monday, Hussein said, they all were dressed in civilian clothes and had been shot in the head and chest.

Separately, police patrolling a south Baghdad neighborhood on Sunday found 18 men who had been handcuffed, blindfolded and shot in the head and chest, Hussein said.

All 46 were believed to have been Sunni Arabs, he said.

As with previous mass killings of Sunnis, Sunni leaders questioned how killers could have moved dozens of corpses through Iraq's many road checkpoints without discovery by security forces.

"What is very strange is that the Iraqi government has not investigated the increasing violence against the Sunni Arabs," said Hussein Shukur Falluji, a leading Sunni politician. "We believe that elements from the government's security forces are involved in this, cooperating with the killers."

Meanwhile, insurgent attacks killed 13 Iraqi policemen Tuesday. In Kirkuk, an oil-rich city 160 miles north of Baghdad, a bomb exploded as a police patrol traveled down a street in the city center. Four policemen were killed and four were wounded, said Sheerzad Abdullah Hasan, a security official in the city. Shortly afterward, he said, three gunmen in a car opened fire on another police patrol, killing four members of the Interior Ministry's emergency forces.

In Baghdad, a bomb outside a restaurant killed four policemen as they gathered over their breakfast of omelets, cheese and tea, officials said.

And in Mosul, a Sunni-dominated city 220 miles north of the capital, police and insurgents battled for about an hour in one neighborhood, leaving one policeman dead and seven wounded, police Maj. Muhammed Ahmed Jubouri said.

U.S. Marines and Iraqi forces in western Iraq, meanwhile, pressed their 11-day-old campaign against insurgent strongholds near the Syrian border. Operation Steel Curtain, which follows more than a dozen military operations conducted in the same area since late April, broadened this week to the area around the town of Ubaydi. Foreign and Iraqi insurgents are believed to have taken refuge there after offensives chased them out of other western towns, the military said.

Strong insurgent resistance Monday and Tuesday apparently "is due in large part to the fact that insurgents believe they are trapped and have nowhere else to go," the U.S. military said in a statement.

U.S. forces said they had killed 80 alleged insurgents since entering Ubaydi. Most of the insurgent killings were inflicted by U.S. military aircraft, the military said. Bombs and small-arms fire killed three Marines in the area, bringing the number of American deaths in the operation to five, the military said. About 2,500 U.S. Marines, soldiers and sailors and 1,000 Iraqi soldiers are participating in the operation.

Correspondent Ellen Knickmeyer in Baghdad and special correspondent Dlovan Brwari in Mosul contributed to this report.

An Iraqi woman wails near the wreckage left by a car bomb that killed four Iraqi policeman as they gathered for breakfast at a Baghdad restaurant. In all, 13 policemen were killed Tuesday in ambushes and bombings across Iraq.