BAGHDAD - Iraqi commandos swept into a western Baghdad neighborhood yesterday and arrested a reputed leader of the al-Qaeda in Iraq group suspected of plotting the assassination of a prominent Sunni lawmaker.

Officials said the suspect was also a member of a government-backed Sunni paramilitary group that has joined forces with the Americans against al-Qaeda in Iraq, but that could not be confirmed.

The brazen daylight shooting death of Harith al-Obeidi raised troubling questions about security just two weeks before U.S. troops are to withdraw from urban areas, and officials have been eager to find those responsible. The gunman died at the scene upon detonating a grenade.

Iraqi forces wearing black masks and helmets stormed the suspect's house in the mainly Sunni neighborhood of Ghazaliyah while he was eating lunch with his wife and three children.

The troops met no resistance as they handcuffed and blindfolded the man, searched the house, then escorted him to their humvees nearby. The operation lasted about 15 minutes, according to an Associated Press photographer at the scene.

The commandos were tipped off by the owner of the murder weapon - who gave them the suspect's name after being arrested, a top Iraqi security official said, speaking on condition of anonymity because he was not authorized to release the information.

Brig. Gen. Numan Dakhil Jawad, commander of the quick-reaction force that staged the raid, said the suspect, Ahmed Abid Uwaid, was believed to be a deputy in the al-Qaeda front group, the Islamic State of Iraq.

Uwaid had continued his insurgent activities even as a member of the local Awakening Council, Jawad said.

Awakening councils, which include former insurgents, joined forces with the Americans, promising to renounce violence and fight al-Qaeda. The movement was initially funded by the Americans.

The Shiite-led Iraqi government has assumed oversight of the groups, drawing complaints about missed monthly payments and crackdowns against their leaders.

Obeidi and a bodyguard were shot dead as they left a mosque Friday in a heavily guarded area in a former insurgent stronghold.

The 47-year-old lawmaker was at the center of a stormy parliamentary debate over claims of torture in Iraqi jails, and some lawmakers had raised suspicion that his slaying may be linked to his campaign on behalf of detainees.