A mini bus carrying a bomb exploded outside an army recruiting center in Baghdad and killed 16 people Monday, the deadliest of a string of attacks that left 29 Iraqis dead. A U.S. soldier also died over the weekend.

The mini bus exploded near the northern gate of the al-Muthana recruiting center in central Baghdad, said defense ministry spokesman Maj. Gen. Ibrahim al-Obeidi. Seven people were also wounded.

A botched car bombing against a U.S. military convoy in eastern Baghdad killed four Iraqis and wounded three, but injured no Americans, said police Maj. Hamid Mousa.

A U.S. soldier was killed by small arms fire Sunday after his patrol came under attack north of Baghdad, the U.S. military command said Monday.

Gunmen killed at least nine people in separate attacks overnight and Monday morning in northern Iraq and in the capital, authorities said.

CountryWatch: Iraq

Assailants opened fire at a telephone exchange center in a commercial Baghdad area early Monday employees started work, killing a man and a woman, said police.

Late Sunday night, two policemen died in clashes with gunmen in southern Baghdad, police said.

In northern Iraq, gunmen in two cars ambushed a bus carrying oil employees from Beiji, the country's largest refinery, killing four people and wounding one, police said.

Iraq's oil infrastructure is frequently targeted by insurgents who blow up pipelines and target oil workers. The country has struggled to resume oil production to prewar levels of about 2.5 million to 3 million barrels a day.

Oil Minister Hussain al-Shahristani said in Vienna the government would bolster its security.

"We already have a military presence there and we're going to reinforce it," al-Shahristani told reporters at a meeting of the Organization of Petroleum Exporting Countries.

In eastern Baghdad, authorities found the bodies of two men dumped in the street in the al-Ubaidi district. Both bodies had their hands and feet tied and had been shot in the head and chest.

A boycott by several political groups again forced parliament to put off a rancorous debate on a bill that Sunni Arabs fear will split Iraq apart and fuel sectarian bloodshed.

The bill, submitted by the Shiite United Iraqi Alliance, calls for a three-part federation that would create a separate autonomous state in the predominantly Shiite south, similar the Kurd-run zone in the north.

Many Sunni Arabs, whose minority dominated during Saddam Hussein's regime, are horrified by the idea. Both the north and south are rich in oil, and Sunnis fear they will end up squeezed into Baghdad and Iraq's western provinces, which have no natural resources.

Vehement objections from Sunni Arabs and an apparent split among Shiites led leaders to delay debate until Sept. 19. A previous attempt to discuss the bill Thursday set off acrimonious squabbling that prompted parliament speaker Mahmoud al-Mashhadani to call a recess.

The Iraqi Accordance Front, the largest Sunni bloc, and another Sunni party, the National Dialogue Front of Saleh al-Mutlaq, boycotted Sunday's parliament session to protest the bill.

They were joined by the secular Iraqi National List led by former prime minister Ayad Allawi and by lawmakers loyal to radical Shiite cleric Muqtada al-Sadr, whose bloc usually supports the United Iraqi Alliance.

"Federalism is a preliminary step to dividing and separating Iraq. I call on Iraqis to confront this draft," said Adnan al-Dulaimi, head of the Iraqi Accordance Front.

Parliament's Shiite deputy speaker, Khalid al-Atiya, defended the bill, denying federalism was meant to destroy Iraq's unity.

The idea that the legislation will divide the country "is a misleading one and agitates public opinion without any reason," al-Atiya told reporters. "Issuing legislation for federalism doesn't mean that we will start the measures of establishing autonomous regions the next day."

The concept of federalism is enshrined in the new Iraqi constitution, and there is already an autonomous Kurdish region in the north. However, special legislation and a referendum would be needed to turn Iraq into a full federation.

There were indications, meanwhile, that a joint U.S.-Iraqi security operation in Baghdad could be expanding into the sprawling Shiite slum of Sadr City, home to more than 2.5 million people and a stronghold of al-Sadr.

Residents said American forces accompanied by Iraqi police patrols drove through five of Sadr City's 79 districts and urged people through loudspeakers to allow searches of their homes. No searches took place, however.

The Defense Ministry said last week that Sadr City would be searched as part of Operation Together Forward, which has put an extra 12,000 Iraqi and U.S. soldiers in the capital to stem rising sectarian violence.