Four people were killed in clashes among rival Shiite militias in the southern Iraqi city of Basra that took place overnight and on Thursday morning, local security officials said.

It was the latest violence to hit the country in a political crisis that pits followers of the powerful Shiite cleric Muqtada al-Sadr against mostly Iran-aligned parties and paramilitary groups.

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

Security forces deployed en masse to quell the fighting, and Basra Governor Assad al-Eidani said Thursday morning that the situation in the city was now "safe and under control."

The exchange of fire triggered panic only days after clashes between al-Sadr supporters and rival Iran-backed factions turned Baghdad's highly secure Green Zone into a battlefield.

The lives of 30 al-Sadr supporters were lost in the nearly 24 hours of clashes that erupted on Monday after they stormed the government headquarters in the Green Zone, which houses state institutions and foreign embassies.

The attack in Basra drew strong condemnation from al-Sadr representative Mohammed Saleh al-Iraqi, who lashed out at Qais al-Khazali, head of the Asaib Ahl al-Haq force.

"I warn you, Qais! If you do not restrain your insolent militias and if you do not absolve yourself of the murderers and criminals that are affiliated to you... you too are insolent," he said in a statement on Twitter.

Violence once again erupted in Iraq this week as armed supporters of al-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 Shiite 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.