A suicide bomber has killed three members of the elite Iraqi police unit in which he reportedly once served after walking into its Baghdad base.
Bombs are virtually a daily occurrence in Baghdad
The government described it as a failed bid to assassinate the prominent head of the Wolf Brigade commando unit, Abul Waleed, who escaped the blast unhurt.
The bomber was identified as a former commando and two other ex-members are reportedly being sought by police.
Gunmen also killed 10 labourers on a minibus travelling towards Baghdad.
Two cars pulled up and militants inside opened fire on the bus, which was coming from the town of Jbala, 70km (45 miles) south of the capital, police said.
Another three workers were injured in the attack, Reuters news agency reports.
Wolf Brigade commandos were recently moved to Baghdad from the northern flash-point city of Mosul in response to mounting attacks by rebels.
Sunni Iraqis, among whom the rebels have their power base, have accused the unit of being heavily pro-Shia and of deliberately targeting Sunnis.
The bomber was unable to reach Abul Waleed "so he blew himself up in the courtyard", Iraqi Interior Minister Baqir Solagh said.
He had managed to slip into the base along with the morning shift, the minister added.
Mr Solagh denied the brigade had been "infiltrated". He was quoted by Reuters news agency as saying a hunt was on for two other ex-members.
A fourth commando was injured in the blast.
Abul Waleed, the name by which Iraqis commonly know Mohammed Qureishi, has become a prominent figure in the campaign against the insurgents, inspiring a popular TV show on which suspects are shown "confessing" to the camera.
Also on Saturday, US troops shot dead two Iraqis in Baghdad's Shula district after they reportedly ignored a warning shot to move their car away from a vehicle patrol.
An Iraqi police officer in the city said that the two were security guards who were killed by mistake.
On Friday evening, a car bomb rocked a market area of Shula, killing 10 and injuring 27.
Seven men, three women and a child were killed, a police source said.