About 30,000 new US troops around Baghdad have not curbed violence
The police in the town of Samawa said the fighting broke out on Thursday with militiamen loyal to the Shia cleric Moqtada Sadr.
Also in southern Iraq, four Iraqi soldiers were killed by a roadside bomb near the town of Hilla.
In south Baghdad, a car bomb exploded on Thursday night, killing 15 people, including a group of wedding guests.
Three children were among the dead. About 27 people were injured, including the bride and groom.
The explosion occurred in front of a photo studio in Abu Dshir where the wedding party had gathered for pictures.
Several nearby shops and businesses were badly damaged in the blast.
Abu Dshir is a Shia enclave in Baghdad's lawless, mainly Sunni, neighbourhood of Dora.
In other developments:
- The US-led coalition in Iraq is deploying hundreds of troops from the Eastern European nation of Georgia to eastern Iraq, to try to halt the flow of deadly weapons from Iran. The Georgians will be deployed in Wasit province, trying to detect Iranian-designed roadside bombs. Iran denies supplying weapons to Shia militants
- An al-Qaeda militant has been executed for his role in a car bombing that killed a leading Shia figure in 2003, a justice ministry official told the Associated Press. The militant, Oras Mohammed Abdul-Aziz, was hanged in Baghdad on Tuesday, the official said.
The execution was the first word of any trial concerning the killing of Ayatollah Mohammed Baqir al-Hakim, the leader of the Supreme Council for the Islamic Revolution in Iraq, and 84 others in Najaf
- Across Baghdad a total of 24 unidentified bodies were found by Iraqi police on Thursday
- A US soldier died of wounds inflicted during fighting on Thursday in west Baghdad, the US military said. Two other US soldiers died on Thursday in southern Baghdad, it said
US and Iraqi forces are currently undertaking a major military operation in the Baghdad area aimed at curbing sectarian unrest.
Some 30,000 extra US troops have now been deployed to Iraq to try to reduce the violence.Popular markets have been walled off, streets closed and the number of checkpoints has been stepped up in an attempt to thwart car bomb attacks.