Shouting for revenge after the slaying of 14 Shia workers, black-clad militias killed at least 31 people in a spasm of sectarian violence in a town north of Baghdad, police, doctors and local residents said on Sunday.
There was also violence in the restive northern oil city of Kirkuk on Sunday, where four car bombs, three of them detonated in suicide attacks, exploded in quick succession, killing 10 people and emptying the streets as terrified residents stayed indoors.
US and Iraqi troops patrolled the city as helicopters hovered overhead. In one of worst attacks, a suicide bomber blew up his car outside a teachers' institute for women, killing four people. They included two students who had been standing at the main gates and were burnt beyond recognition.
Three US soldiers were killed by a roadside bomb south of Baghdad, the US military said, adding to a toll that, at the current pace, could make October the deadliest month for US forces since January 2005. Nearly 60 have been killed so far.
In the town of Balad, 80 km (50 miles) north of Baghdad, the weekend killings were swift and brutal. Militiamen riding in pick-up trucks set up fake checkpoints on Saturday, stopping vehicles and checking IDs in response to the killing of the workers, whose bodies were found on Friday in an orchard with their throats slit and hands and legs bound.
Some of the bodies brought to the hospital in the last 24 hours were mutilated and bore signs of torture from what appeared to be reprisal sectarian attacks across Balad, a mostly Shia town surrounded by Sunni areas.
Qasim al-Qaisi, head of Balad hospital, said most of the bullet-riddled bodies were Sunni Arab men. The Shia labourers, who were from Balad, were found in nearby Dhuluiya, a mostly Sunni town across the Tigris River.
"We are preparing ourselves to receive more bodies as long as the situation can get worse," Qaisi told Reuters. "Sectarian killing is sweeping the area."
Gunmen were roving Balad and manning checkpoints on Sunday and residents said the town was tense. Hamad al-Qaisi, governor of central Salaheddin province, travelled to Balad along with the province's police chief to restore calm, officials said.
Prime Minister Nuri al-Maliki, struggling to contain soaring communal violence that threatens to plunge Iraq into civil war, used the one-year anniversary of a referendum for a US-backed constitution to renew a pledge to disband militias.
US officials say militias pose a graver danger to Iraq's survival than a three-year old Sunni insurgency. But disbanding them is delicate because they are tied to political parties.
Hours before he spoke, gunmen killed a Shia family of eight in their home in Latifiya, in the Sunni "Triangle of Death" south of Baghdad. The dead were three women, two children and three men.
A government official survived an assassination attempt when a roadside bomb went off near her convoy in eastern Baghdad, killing four bystanders, the Interior Ministry said.
Roadside bombs are also responsible for most of the deaths among US troops in Iraq.