Broken glass remains at the scene of a suicide bomb attack at Adan Square, located in a predominantly Shiite part of the capital, Baghdad, Feb. 9, 2015.

A prominent Iraqi Sunni tribal leader and his son were killed late on Friday in an attack on their convoy in south Baghdad, raising questions about security in the capital and threatening to exacerbate sectarian tensions.

Security and political sources said Sheikh Qassem al-Janabi and his son, Mohammad, were shot dead along with at least six guards after gunmen stopped them on the way back from their home in Latifiya, a city south of Baghdad.

The sheikh’s nephew, parliamentarian Zayed al-Janabi, was also detained but later released, the sources said.

Interior ministry spokesman Brigadier-General Saad Maan told state television the ministry would investigate the incident.

No group has claimed responsibility for the attack, but Deputy Prime Minister Saleh Mutlaq called for curbs on Shi’ite armed groups, which operate freely in many areas and have spearheaded the battle against Islamic State of Syria and Iraq (ISIS) insurgents after the army nearly collapsed last summer.

“We must get rid of the militias, and weapons must be in the hands of the state,” Mutlaq told reporters before the men were buried on Saturday.

“They want to bring down… the voice of every patriot. This is a message we must understand: to take a stand against the militias and the outlaws.”

Prime Minister Haider al-Abadi last week ordered the end to a long-standing curfew in Baghdad as well as a reduction of checkpoints and limits on weapons in some districts. Critics say that move was premature.

Abadi, a moderate Shi’ite Islamist who has sought reconciliation between Iraq’s Shi’ite and Sunni communities, has also pledged to crack down on alleged abuses by security forces and paramilitary groups operating in areas regained from ISIS.

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