The US military has accused Iranian-backed Shia groups of setting off a car bomb that killed more than 60 people in a mainly Shia area of Baghdad, hinting at yet another new twist in the complex web of violence gripping the capital.

“We believe the attack was not conducted by AQI [Al-Qaeda in Iraq],” said Lieutenant-Colonel Steven Stover, a US army spokesman, said. “Though vehicle-borne improvised explosive devices are a trademark of AQI, our intelligence, corroborated through multiple sources, is this atrocity was committed by a Special Groups cell led by Haydar Mehdi Khadum al-Fawadi.” The Special Groups are rogue elements of al-Mahdi Army, the Shia militia of the anti-American cleric Hojatoleslam Moqtada al-Sadr, which have allegedly been co-opted by the Iranian Revolutionary Guards overseas division, the al-Quds Force. Colonel Stover said that the aim of the bombing was to discourage Sunnis from returning to the predominantly Shia area of al-Hurriyah in northwestern Baghdad and sow sectarian strife as the levels of violence drop in the divided city.

He added that another goal of preventing Sunnis returning to homes they had been chased from by Shia militias was “to maintain extortion of real estate rental income to support his nefarious activities.” Many Sunni families trying to return to their homes have complained that Shia militias have either settled Shia refugees from Sunni-dominated areas in their homes, and collect rent, or try to sell the properties themselves.

Special Groups and Shia death squads have been blamed for mass kidnappings in which the victims — often dozens at a time — were massacred in recent years. The latest claim was the first time that the military has overtly accused them of adopting the car bombing tactics of al-Qaeda.

Colonel Stover said that the type of vehicle and explosives used led the military to believe al-Qaeda was not behind the car bomb, which ripped through a crowded evening market. Among the dead were four children and five women, police said.

Al-Qaeda once launched almost daily bombings against civilian targets in Iraq but has been undermined after its bloody tactics alienated its Sunni insurgent supporters, tens of thousands of whom have now joined US-backed Awakening groups to protect their neighbourhoods from terrorists.

Major-General Kevin Bergner, another military spokesman, said that Iraqi and US intelligences forces were assessing whether the “Shia-on-Shia” bombing marked the beginning of a new wave of violence in Iraq’s ever-shifting conflict.

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