A suicide bomber blew himself up among a crowd of poor Shiite Muslim laborers waiting for work in Baghdad early Wednesday, the Interior Ministry said. News agencies cited police as saying at least 80 people were killed and more than 150 were injured.

The bombing followed a week of relative calm in the capital. Television footage showed victims lying on the floors of hospitals, wincing in pain. Iraqi security forces and women in black abayas ran among the twisted, blackened frames of cars, peering inside for victims.

The blast occurred in the heavily Shiite neighborhood of Kadhimiyah, which is usually crowded with students and government workers, as well as day laborers looking for work.

While there was no immediate assertion of responsibility, the attack bore the hallmark of Abu Musab Zarqawi's insurgent group, al Qaeda in Iraq, which is dominated by Sunnis. The group has called Shiite civilians apostates and declared them legitimate targets.

Authorities did not provide a definitive death toll, but Col. Adnan Abdul Rahman, spokesman for the Interior Ministry, said the number was on the rise.

Also Wednesday, police said gunmen dragged 17 people out of their homes just north of Baghdad and killed them, according to Reuters. Police said the gunmen rounded up their victims in the middle of the night and shot them outside their houses in Taji.

In Baghdad, insurgents on Tuesday fired two mortar shells inside the Green Zone, the sprawling, fortified base that houses the Iraqi government and foreign diplomatic and military facilities. The rounds exploded near a military hospital, setting off sirens and creating confusion. There were no reports of casualties.

Elsewhere in the capital, insurgents ambushed and killed two truck drivers delivering concrete blast walls that were intended to protect against bombs. In a separate incident, the body of a former judge was found with a note that read: "This is the destiny of those who support Saddam," the Associated Press reported.

Near the southern Shiite Muslim city of Basra, a roadside bomb injured three private security contractors, a Western official said. The city, dominated by leaders of various Shiite factions, has been jolted in recent weeks by repeated bombings targeting Americans, Britons and others.

In Baqubah, about 35 miles northeast of the capital, gunmen shot and killed two Sunni Muslim clerics, and in Hilla, about 60 miles south of Baghdad, a bomb exploded on a bus, killing two civilians, news agencies reported.

U.S. warplanes attacked the western town of Haditha, one of several communities along the Euphrates River that are dominated by foreign and Iraqi insurgents. U.S. forces said they killed four suspected insurgents and detained a man with suspected ties to al Qaeda.