Iraqi security forces at a new base in the working-class neighborhood of Amil spent Monday belatedly constructing a barrier of bricks and concrete blocks hours after a suicide bomber drove a vehicle packed with explosives straight into the building where the men were housed, witnesses said.

Once inside the former factory, the driver detonated his cargo, killing himself and ending a three-day lull in such attacks in the capital.

The full extent of the casualties from the Monday morning attack was unclear; al-Arabiya television reported that five people were killed, but the Associated Press quoted a police official saying three policemen and three bystanders were wounded. Police at the scene declined to comment.

The Iraqi forces "only moved there three days ago, so they did not have any concrete barriers or obstacles or any kind of security or reinforcements for the building yet," said Ali Jabur, who works next door to the new base. "That is why this suicide bomber was able to drive directly from the main street to the building. They shot at him -- I heard that, they tried to stop him -- but he did not stop and continued right inside."

The level of violence in Iraq remained relatively low, however, and officials continued to attribute the lull to an ongoing security crackdown called Operation Lightning.

The U.S. military said Monday that an American soldier was killed Sunday in a roadside bombing near the northern city of Kirkuk. And in Kirkuk early Monday, unidentified gunmen shot and killed an Iraqi man, Mohammed Ghazi, who neighbors said had worked closely with U.S. forces in the city. A U.S. military spokesman confirmed that there had been a fatal shooting in Kirkuk but said he had no information on the victim.

In Baghdad, Iraqi political leaders continued their efforts to involve more members of the Sunni Muslim minority in a new government led by Shiite Muslims. With the committee drafting Iraq's permanent constitution set to meet again Thursday, Sunni Arab leaders were weighing a proposal that would allow them to add 14 or 15 new members to its ranks, according to a Sunni political leader involved in the discussions.

The 55-member committee currently has just two Sunni members because it is drawn from Iraq's National Assembly, which is dominated by Shiite Arabs and Sunni Kurds. Sunni Arabs, who make up an estimated 15 percent to 20 percent of Iraq's population, largely boycotted elections in January.

Kurdish members are pushing an alternative proposal that would expand the committee to about 100 members.

Under existing rules, only the original 55 committee members have voting rights, but the panel's leaders could rule that all decisions will be made by consensus or legislation could be passed to allow new members to vote.

The committee must complete a draft constitution by Aug. 15 or take a six-month extension that would delay the nationwide referendum on the document, scheduled for October.

"If decisions are made by consensus, then the numbers don't matter so much," said Saleh Mutlak, the Sunni leader involved in the discussions. "But to get an agreement by consensus on anything in such a short period of time might be an excuse to get an extension. That would be a bad thing. We want the government to finish as soon as possible."

The bombing Monday in Amil, a neighborhood on Baghdad's west side, could easily have been more devastating than it was, residents said. The explosion spewed flaming wreckage and shrapnel 150 yards, but none of it apparently caused serious damage to the girls' high school across the street or to Jabur's business -- a government-run facility for dispensing cooking fuel. If the wreckage had hit any of his four huge gas tanks, Jabur said, "it would be worse than a nuclear bomb."

Jabur said he has worked at the same location since 1991. Before last week, he said, the factory next door had housed squatter families, and it once produced furniture for the government of Saddam Hussein. His new neighbors posed dangers he hadn't faced before. "If they will not move from here, I will quit working here," Jabur said.

Another local resident, Modhafir Fadhil, said Monday was the day for final exams at Madhil High School across the street. "Can you imagine what happened to those girl students when they were taking the exam?" he said.

Fadhil, 52, said he lives in an apartment building adjacent to the new base. "I do not know where to go now," he said. A nearby police station has been a frequent target of insurgent attacks, "and now this base across the street. I will be living in a battlefield."

Correspondent Jonathan Finer in Baghdad and special correspondent Marwan Ani in Kirkuk contributed to this report.

Members of the Iraqi Interior Ministry's Falcon Brigade briefly detain and question three men in western Baghdad outside the brigade's base, where a suicide bomber detonated his vehicle.