U.S. and Iraqi troops arrested about three dozen people connected with one of the top Sunni politicians, including his son and a security guard. Military officials claimed they had keys to a suicide car bomb.
Five American soldiers and an Iraqi civilian were injured trying to detonate the explosives near the compound of Adnan al-Dulaimi, leader of the biggest Sunni bloc in parliament, the U.S. military said in a statement.
The mass detention of al-Dulaimi's staff and his son threatened to inflame political tensions between Sunni politicians and the Shiite-dominated government. Al-Dulaimi is a harsh critic of Prime Minister Nouri al-Maliki.
Brig. Gen. Qassim al-Moussawi, the chief Iraqi military spokesman in Baghdad, said Maki Adnan al-Dulaimi, the senior lawmaker's son, was arrested after a gunman fleeing U.S. and Iraqi troops sought refuge in his father's office Thursday night.
Al-Moussawi said two car bombs were discovered at the al-Dulaimi's office compound.
The U.S. statement said one vehicle rigged as a suicide car bomb was found on the street outside the compound, and one of al-Dulaimi's security guards had the keys.
According to the U.S., the pursuit involved two gunmen, and more than 40 people were detained in the investigation; the Iraqi officer said 36 people were being held.
The senior al-Dulaimi was under guard from his home in Baghdad.
"A joint U.S.-Iraqi force came to my house at dawn and they arrested my son and now all family members are not allowed to leave the house," the lawmaker said from his home in Adil neighborhood.
Al-Moussawi said the guard was in place to protect al-Dulaimi and his family members from reprisal. Al-Dulaimi said he thought otherwise.
"I will wait until Saturday morning and if the ban on my family continues, then I will consider the government's measure as a house arrest," he told The Associated Press.
Al-Dulaimi frequently accuses the Shiite al-Maliki of following sectarian policies. He is the leader of the Iraq Accordance Front, parliament's largest Sunni Arab bloc with 44 of the house's 275 seats. The Front pulled out its Cabinet members from the government in August to protest the prime minister's policies.
Al-Moussawi declined to specify the charges against Maki al-Dulaimi.
The gunmen who allegedly sought refuge in the Sunni politician's office were responsible for the death of an Iraqi serving as a member of U.S.-backed neighborhood watch group that is fighting extremists, the U.S. statement said. The watch groups, which are credited with helping curb violence, grew out of a Sunni rebellion against al-Qaida in Iraq in the former insurgent stronghold of Anbar province and are considered one of the main success stories in more than four years of war.
Separately, a four-day U.S. operation outside Beiji, 250 kilometers (155 miles) north of Baghdad, U.S. forces detained 18 suspects and found two weapons caches after reports that al-Qaida in Iraq was using the area to plan attacks, the U.S. military said in a statement Friday.
In other operations late Thursday and Friday in central and northern Iraq, the military said, one terror suspect was killed and 17 captured.
Also Friday, Deputy Secretary of State John Negroponte continued a visit to Iraq, where he was expected to meet with both Iraqi and American officials.
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