The skirmishes are the latest violence to hit the country in a political crisis that pits followers of the powerful Shi'ite cleric Moqtada al-Sadr against mostly Iran-aligned parties and paramilitary groups.

The security officials said the clashes took place in the centre of Basra, Iraq's main oil-producing hub. Two of those killed were members of Sadr's Peace Brigades militia, they said.

Violence re-erupted in Iraq this week as armed supporters of Sadr fought with security forces and Iran-aligned gunmen in Baghdad in the fiercest street battles the capital has seen for years.

An intractable political deadlock between the two rival Shi'ite camps has left Iraq without a government since an October election.

It has also deepened dysfunction and instability as Iraqis struggle to move on from decades of war, sanctions, civil strife and endemic corruption.

Australian Associated Press