Earlier, Karbala Gov. Akeel al-Khazaali had reported that US troops raided the provincial headquarters looking for wanted men but left with no prisoners. But Brooks said that report was incorrect.

The general did not identify any group suspected of staging the attack, but residents reached by telephone had reported seeing military helicopters flying over the local headquarters of radical Shiite cleric Muqtada al-Sadr.

Al-Sadr's Mahdi Army militia, which has been accused of playing a big role in sectarian killings, has been hit repeatedly in recent weeks by operations in which key commanders have been captured or killed by US and Iraqi troops.

Also Saturday, roadside bombs killed a soldier in the capital and one in Nineveh province north of Baghdad.

The US military also announced that combat Friday had killed an Army soldier in Nineveh province and a Marine in Anbar province, a Sunni insurgent stronghold west of the capital. The Marines often delay death reports, raising the possibility that Friday's toll was higher.

The helicopter crash was the fourth deadliest since the start of the war. The worst crash occurred on the war's deadliest day, Jan. 26, 2005, when a Marine transport helicopter crashed during a sandstorm in Iraq's western desert, killing 30 Marines and a sailor. On the same day, six other US forces died in combat for a total of 37 deaths.

The second highest daily toll was on March 23, 2003 when 28 service members were killed as American forces were pushing toward Baghdad on the third day of the US-led invasion.

Meanwhile, the first reinforcements of US troops under the new Bush strategy have already started to flow into the Baghdad region. A brigade of the US 82nd Airborne Division, part of the buildup, has arrived in Baghdad and will be ready to join the fresh drive to quell sectarian violence in the capital by the first of the month, the American military said Sunday.

The 2nd Brigade of the 82nd Airborne consists of about 3,200 soldiers who will "assist Iraqi Security Forces to clear, control and retain key areas of the capital city in order to reduce violence and to set the conditions for a transition to full Iraqi control of security in the city," the military said in a statement.

In south Baghdad, US helicopters dropped Iraqi police commandos into the dangerous Dora neighborhood to stage a raid on the Omar Brigade, an al-Qaida-linked Sunni militant group, Interior Ministry spokesman Abdul-Karim Khalaf said.

Khalaf said 15 insurgents were killed and five captured during an intense battle at two abandoned houses taken over by Sunni gunmen, who he blamed for a series of kidnappings and killings in a bid to cleanse the once-mixed neighborhood of Shiite residents.

"We were provided with helicopter support by our friends in the multinational forces and we did not suffer any casualties," Khalaf said. US aircraft gave covering fire, but the US military did not respond to a request for comment on the raid.

Elsewhere in Baghdad, Iraqi police and hospital officials said a joint US-Iraqi force searched a hospital in the volatile Sunni-dominated western neighborhood of Yarmouk.

Dr. Haqi Ismail, the hospital manager, said the raid occurred at 4:30 a.m.

"They were looking for someone, they searched all the rooms and the emergency unit," he said.

Al-Sadr's followers voiced increasing anger over Friday's capture of a senior aide to the radical cleric in a raid in eastern Baghdad.

Nassar al-Rubaie, the head of al-Sadr's bloc in parliament, accused US forces of trying to provoke the Sadrists into violence during the expanding campaign to quell Iraq's fighting.

"We condemn strongly the arrest of Sheik Abdul-Hadi al-Darraji. He is moderate and well-known as a media personality and always available in negotiations," al-Rubaie said. "He is a peaceful man and what was mentioned in the American release is lies and justification for the aggression against al-Sadr's movement."

US and Iraqi forces reportedly detained al-Darraji during a raid on a mosque complex before dawn Friday.

The US military, in a statement that did not name al-Darraji, said special Iraqi army forces operating with US advisers had "captured a high-level, illegal armed group leader" in Baghdad's Baladiyat neighborhood, next to the Mahdi Army stronghold of Sadr City. It said two other suspects were detained for further questioning.

Sadiq al-Rikabi, an al-Maliki adviser, told Al-Arabiya television the operation was not coordinated with Iraq's political leaders and was not part of the new security campaign.

Police reported at least 16 Iraqis slain in attacks Saturday. In addition, officials said 29 bodies were found in Baghdad and three in the northern city of Mosul, most of them showing signs of torture - a hallmark of killings by sectarian death squads.

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