The fighting erupted as rival visions of how to halt the carnage in Iraq went on show, when US troops built walls around a restive suburb of Baghdad and a regional Shiite leader announced a plan to set up local militias.
In the northern city of Mosul, a truck bomber targeted the regional offices of the Patriotic Union of Kurdistan, President Jalal Talabani's party, and the Peshmerga Kurdish militiamen who guard the building.
"Eight Peshmerga were killed and 51 others wounded in the attack," said Ziriyan Othman, health minister of the Kurdish administration in northern Iraq.
In Baghdad, US and Iraqi forces are trying to restore the battered authority of Iraq's coalition government by sweeping city districts for weapons and isolating protected areas behind checkpoints and concrete barriers.
Private militia
But in the holy city of Najaf, which last week was the scene of a deadly bomb attack outside a major Shiite shrine, local leaders said they would take matters into their own hands and authorise neighbourhood militias.
"We started today forming a committee in Najaf to choose individuals who will control security in their neighbourhoods and keep an eye on all suspicious movements in their areas," deputy governor Abdul Hussain Abtan said.
"This will be done in collaboration with security forces in the city and is the first step in activating popular committees," he said, in a move that will be seen as a snub to the government of Prime Minister Nuri al-Maliki.
Since February, when suspected Sunni bombers destroyed the golden dome of a holy Shiite mosque in Samarra, insurgent attacks and sectarian death squads have killed thousands of Iraqis in a string of tit-for-tat murders.
In another sign of the danger posed by Iraq's private armies, Iraqi security forces have clashed in the Shiite city of Karbala with militiamen loyal to a lesser known cleric, Ayatollah Mahmoud al-Hasani.
Two army officers, a soldier and three civilians were killed in the fight, according to a local health official while more than 200 militiamen were arrested in a raid on Ayatollah Hasani's office.
But despite the arrests, Ayatollah Hasani called upon his followers to carry on the fight, according to Al-Zahra television, after which the police imposed a three-day curfew in the city, banning any movement of people or vehicles.
Baghdad security
US commanders fear mounting sectarian violence and the proliferation of local militias could push Iraq into all-out civil war, and have launched their own drive to protect vulnerable populations.
In Baghdad, the joint US-Iraq operation "Together Foward" has brought 10,000 US troops and 50,000 government security forces on to the streets of the city.
The US military said the Dura district of southern Baghdad had been walled in behind concrete barricades and fortified check points.
The US military also retracted an earlier statement, which blamed a series of explosions in Baghdad Sunday on an accidental gas explosion, and confirmed Iraqi reports that the carnage had been triggered by car bombs.
An Iraqi spokesman said the death toll from these blasts had risen to 73.