Security and hospital officials in Iraq say the death toll in the suicide bomb attack on a campaign rally for supporters of a Shiite militant group has risen to 33.

They said Friday's attack at a sports stadium in eastern Baghdad also injured 40 people.

The officials spoke Saturday on condition of anonymity because they were not authorized to brief journalists.

An al-Qaida breakaway group, the Islamic State of Iraq and the Levant, claimed responsibility for the attack at the rally, which drew about 10,000 supporters of the Iranian-backed Asaib Ahl al-Haq group.

It said the bombings were revenge for the killing of Sunnis and their forced removal from their homes by Shiite militias.

Iraq votes Wednesday in a parliamentary election, its first since U.S. troops withdrew in 2011.