Underlining the variety of deadly challenges facing the 100-day-old national unity government of Prime Minister Nuri al- Maliki, a suicide car bomber in Baghdad killed 13 policemen and wounded 62 other people outside the Interior Ministry.
Maliki has vowed to disarm all militias, including those of fellow Shi'ite Islamists with seats in the coalition cabinet. But US-trained government forces face an uphill task.
The Defence Ministry, local officials and the Mehdi Army of populist young cleric Moqtada al-Sadr gave conflicting accounts of battles overnight and into the day in Diwaniya, a normally placid provincial capital, 180 km (110 miles) south of Baghdad.
A Defence Ministry spokesman in the capital said 20 of its soldiers were killed along with 50 unidentified "gunmen" who had stormed police stations after dark yesterday. A local leader of the Mehdi Army insisted only two of his men had been killed.
An agreement brokered in the nearby clerical city of Najaf between Sadr and the Diwaniya governor, from a party that rivals Sadr within Maliki's dominant Shia bloc, brought an edgy calm by nightfall after hours of mortar, rocket and machinegun fire.
The Baghdad bombing resembled many carried out by al Qaeda and pro-Saddam Hussein militants from the once dominant Sunni minority and was one of the worst in the capital since US and Iraqi troops launched a security clampdown three weeks ago.
Eight US soldiers were among more than 60 people killed yesterday in violence that challenged Maliki's latest assertion his forces had the upper hand and there would be no civil war.
The chief US military spokesman said killings in Baghdad had almost halved this month from last and that car bombings were at an eight-month low, but Major General William Caldwell acknowledged there had been a spike again in the past two days.
Sunni insurgents long posed the main threat to US efforts to install a stable elected government but militia violence against Sunnis and among Shias is now killing more people.