Suicide bombers killed 31 people Friday at a sports stadium hosting a campaign rally for thousands of supporters of a militant Shia group before parliamentary elections, authorities said an attack that could unleash more sectarian violence.

An al-Qaeda breakaway group, the Islamic State of Iraq and the Levant, claimed responsibility for the attack at the Industrial Stadium in eastern Baghdad, which drew about 10,000 backers of the Iranian-backed Asaib Ahl al—Haq group.

It said on a militant website that the bombings were to avenge what it called the killing of Sunnis and their forced removal from their homes by Shiite militias.

The authenticity of the claim could not be independently verified.

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