U.S.-led strike forces seized suspected Shiite death squad bosses Tuesday in raids that tested the fragile bonds between the government and a powerful militia faction allowing the Baghdad security crackdown to move ahead.

The sweeps through the Sadr City slum were part of highly sensitive forays into areas loyal to radical cleric Muqtada al-Sadr, who has ridiculed the 2-week-old campaign for failing to halt bombings by suspected Sunni insurgents against Shiite civilians.

Al-Sadr withdrew his powerful Mahdi Army militia from checkpoints and bases under intense government pressure to let the security push go forward. But the U.S.-backed government of Prime Minister Nouri al-Maliki also worries that al-Sadr could pull his support if he feels his militiamen are being squeezed in Baghdad.

The pre-dawn raids appeared to highlight a strategy of pinpoint strikes in Sadr City rather than the flood of soldiers sent into some Sunni districts.

Bombings have not slackened off, with at least 10 people killed in blasts around Baghdad on Tuesday. However, an apparent success of the clampdown can be measured in the morgues: a sharp drop in the number of bullet-riddled bodies found in the streets of the capital, victims of sectarian death squads.

The number of bodies found this month in Baghdad — most shot and showing signs of torture — has dropped by nearly 50 percent to 494 as of Monday, compared with 954 in January. The figure stood at 1,222 in December, according to figures compiled by The Associated Press.

"We have seen a decrease in the past three weeks — a pretty radical decrease," said Lt. Gen. Ray Odierno, the No. 2 U.S. commander in Iraq.

Many Sunnis have long alleged that most of killings were by Shiite militias, such as the Mahdi Army or rogue elements within the Shiite-led police.

The U.S. military said the raids targeted "the leadership of several rogue" Mahdi Army cells that "direct and perpetrate sectarian murder" — an apparent reference to execution-style slayings and torture. At least 16 people were arrested.

"My sons and wife were very terrified," complained Muhannad Mihbas, 30, who said his brother and six cousins were taken in the sweeps. "Does the security plan mean arresting innocent people and scaring civilians at night?"

Odierno declined to comment on whether there were special tactics governing the Sadr City sweeps. "We will go after anyone who we feel is working against the government of Iraq," he said.

U.S. military spokesman Maj. Gen. William Caldwell told Al-Arabiya television that forces "will increase our operations in the coming days," but noted that the security crackdown in the capital should continue until at least October.

Added Odierno: "We will keep at this until the people feel safe in their neighborhoods."

Also Tuesday, a roadside bomb southwest of the capital killed three U.S. soldiers assigned to a unit based in Baghdad, the U.S. military said. A fourth Ameridan soldier was killed near Diwaniyah, a mostly Shiite town 80 miles south of Baghdad.

Iraqi authorities, meanwhile, have arrested a suspect in the attempted assassination of Shiite Vice President Adel Abdul-Mahdi, an aide said.

The aide said the arrest was made after reviewing security camera video from Monday's blast, which ripped through an awards ceremony at the ministry of public works and killed at least 10 people. Abdul-Mahdi suffered leg injuries.

The aide declined to give any further details about the arrest or the suspect. He spoke on condition of anonymity because he was not authorized to brief the media.

Abdul-Mahdi is one of two vice presidents. The other is Sunni.

In the southern Qadisiya province, Iraqi security forces said they captured 157 suspects linked to a shadowy armed cell called the Soldiers of Heaven, or Jund al-Samaa. The group was involved in a fierce gunbattle last month with Iraqi forces who accused it of planning to kill Shiite clerics and others in the belief it would hasten the return of the "Hidden Imam" — a descendant of the Prophet Muhammad who disappeared as a child in the 9th century. Shiites believe he will return one day to bring justice.

A U.S. Apache helicopter was shot down in the fighting, and two U.S. crew members were killed.

Meanwhile, state television reported that 18 boys were killed when a car bomb exploded in a park in Ramadi, and Iraqi and international officials were quick to deplore the slaughter. But questions about key details of the report emerged just as quickly.

Iraqi police and state TV said the attack occurred Tuesday. Later, police said it happened Monday.

The confusion grew deeper following an announcement by U.S. forces that 30 civilians and one Iraqi soldier were injured by flying debris Tuesday when troops intentionally detonated 15 bags of explosives found in Ramadi.

The news first broke after nightfall when it is too dangerous for local journalists to check the reports independently in Ramadi, a Sunni insurgent stronghold 70 miles west of Baghdad. Western reporters normally tour the area only as part of military patrols. Much of Ramadi is under effective insurgent control, and even the police have difficulty establishing the facts in bombings and assassinations.