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

An al-Qaida 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.