The fighting broke out in Maysan province, with the violence centred in a village some 70 kilometres (45 miles) south of provincial capital Amarah.

Mohammed al-Saray, a forensics department official in Amarah, said eight people had died and a dozen others had been wounded, including women and children.

A security source, speaking on condition of anonymity, said one group had "taken over state-owned agricultural land" and relatives from the same tribe were "demanding an equal share".

In Iraq, where state institutions have been weakened by decades of war, tribes are powerful actors -- particularly in its oil-rich south, where they have their own moral and judicial codes as well as huge caches of arms.

In Maysan, a province bordering Iran, drug trafficking, tribal disputes and political score-settling have combined into a toxic mix.

Violence is a common and police and judicial officials have been regular targets of assassination attempts.

On Monday, police announced a "joint security operation" with the army in Maysan to find those behind the assassination of a tribal chief, Sheikh Mohamed al-Faysali, who was killed outside his home.