U.S.-backed Iraqi forces stormed the Health Ministry and arrested the No. 2 official Thursday, accusing him of links to Shiite death squads and diverting funds to the biggest Shiite militia. The raid served as a litmus test of the prime minister's promise to curb militia power, as four more Americans died in fighting.

Shiite politicians linked to anti-American cleric Muqtada al-Sadr expressed outrage over the arrest of Deputy Health Minister Hakim al-Zamili as a violation of Iraqi sovereignty and demanded that Prime Minister Nouri al-Maliki intercede for his release.

But al-Maliki and his senior advisers remained silent. Al-Maliki is under strong pressure from the U.S. to crack down on militias and has pledged not to interfere in the upcoming security operation to rid Baghdad's streets of militias and insurgents.

Also Thursday, the U.S. announced that four U.S. Marines were killed the day before in fighting in Anbar province, an insurgent stronghold west of Baghdad. The deaths raised to at least 3,114 members of the U.S. military who have died since the Iraq war started in March 2003, according to an Associated Press count.

Iraqi troops pushed through the iron gates of the Health Ministry building in northern Baghdad, ordered people down to the floor and rushed to al-Zamili's ground floor office, witnesses said.

AP Television News footage of al-Zamili's office showed overturned chairs, files scattered on the floor, smashed computers and telephone sets littering the floor.

A U.S. military statement did not mention al-Zamili by name but said Iraqi special troops had captured a "senior official" suspected of "alleged corruption" and links to al-Sadr's Mahdi Army militia. The Health Ministry is among six Cabinet posts controlled by al-Sadr, an ally of the prime minister.

The statement also alleged that al-Zamili played a role in the deaths of several ministry officials, including the Sunni director of health in Diyala province. The director, Ali al-Mahdawi, vanished last June after arriving in Baghdad for a meeting at the ministry.

According to the statement, al-Zamili was believed to have siphoned millions of dollars from the ministry to the Mahdi Army "to support sectarian attacks and violence targeting Iraqi citizens."

U.S. military spokesman Lt. Col. Christopher Garver said militiamen were allowed to use government hospitals and clinics to gather information on Iraqis seeking treatment and "those Iraqis that were discovered to be Sunnis would later be targeted for attacks."

U.S. officials had long complained that al-Sadr's followers were transforming hospitals into bases for the Mahdi militia and were diverting medicine from state clinics to health care facilities run by the cleric's movement.

Those clinics helped al-Sadr build a powerful nationwide political movement modeled in part on the Shiite Hezbollah militia in Lebanon.

But the arrest is likely to add new strains to al-Maliki's fragile coalition as it embarks on a high-risk campaign to curb violence in Baghdad. Shiite politicians persuaded al-Sadr to pull his militiamen back from the streets in the run-up to the security campaign.

But a series of bombings and suicide attacks against Shiite civilians in Baghdad and the southern city of Hillah has led many Shiites to complain that U.S. and Iraqi forces have not launched the security campaign fast enough to protect them against Sunni extremists.

Nasr al-Rubaie, leader of the Sadrist bloc in parliament, called al-Zamili's arrest a "kidnapping."

Health Minister Ali al-Shemari also denounced the raid.

"This is a violation of Iraq's sovereignty," he said. "They should have a court order to carry out a raid like this."

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But U.S. officials have insisted that al-Maliki reign in al-Sadr's forces, and the prime minister told the mercurial cleric last month that he could no longer provide him with political protection in the face of U.S. pressure, according to al-Maliki's aides.

Curbing the militias is considered key to halting the wave of Sunni-Shiite reprisal killings that surged after last year's bombing of a Shiite shrine in the mostly Sunni city of Samarra.

Despite recent efforts, the violence showed little signs of receding.

At least 104 people were killed or found dead Thursday in Iraq, including at least 10 Sunni men gunned down in the village of Rufayaat, just east of Balad. Balad is a majority Shiite town 50 miles northeast of the Iraqi capital, but it is surrounded by territory that is mainly populated by Sunnis.

In the deadliest attack Thursday, a parked car bomb exploded at a food market in the predominantly Shiite town of Aziziyah, 35 miles southeast of Baghdad, killing 20 people and wounding 45, police said.

Another parked car bomb tore through a minibus in the mainly Shiite Amin neighborhood of southeastern Baghdad, killing seven passengers and wounding 10, police said.

Also in Anbar, a U.S. airstrike killed 13 insurgents in a raid on two safe houses where intelligence showed foreign fighters were assembled near Amiriyah, the military said. Five militants were detained and a weapons cache was found in an initial raid on a target near the safe houses.

Police and hospital officials in the area offered a conflicting account, saying the airstrike hit the village of Zaidan south of Abu Ghraib and flattened four houses, killing 45 people, including women, children and old people.

An Associated Press photo showed the body of a boy in the back of a pickup truck at the nearby Fallujah hospital and people there said he was a victim of the Zaydan airstrike. Other photos showed several wounded children being treated in the hospital.

The U.S. Embassy in Baghdad, meanwhile, said U.S. officials were investigating a Jan. 31 incident involving a civilian helicopter after The New York times reported that insurgents had brought the chopper down with ground fire during a flight between Hillah and Baghdad in support of State Department operations.

A Pentagon official, speaking on condition of anonymity because he was not authorized to disclose the information, said the helicopter belonged to the private security firm Blackwater USA and did not crash but rather landed and the people aboard were safely evacuated.

If confirmed, it would be the second Blackwater helicopter and at least the sixth overall to go down in Iraq since Jan. 20, prompting the U.S. military to review flight operations. The most recent crash occurred Wednesday when a CH-46 Sea Knight went down northwest of Baghdad, killing seven people.

Iraqi state run television and an Iraqi official said that security forces detained an aide to the leader of Al Qaeda in Iraq in a raid early Thursday at a gas station south of Baghdad.

The official, speaking on condition of anonymity because he was not authorized to speak to the media, said the aide to Abu Hamza al-Muhajir, also known as Abu Ayyub al-Masri, was one of two men arrested in the dawn raid.

The two suspects ran a gas station in Mahmoudiya, about 20 miles south of Baghdad, on behalf of Al Qaeda in Iraq, the official said, adding the returns from selling gas and other oil products on the black market were being used to finance the operations of local Al Qaeda in Iraq cells.

The official, who was involved in the raid, did not identify the two men, but added that the al-Masri aide had confessed to meeting the terror network leader the previous day in the Mahmoudiya area, but that he could not tell investigators of his current whereabouts because he was constantly on the move.