(CNN) -- Bombers killed at least 31 people and wounded 56 more at a political rally in a stadium in eastern Baghdad on Friday, days ahead of parliamentary elections, two police officials said.
The al Qaeda splinter group Islamic State of Iraq and Syria claimed responsibility, according to a post on a jihadist website.
About 200 people attended the event, sponsored by a Shiite political group, officials told CNN.
A car bomb first hit the gathering. It was followed by a suicide bomber wearing an explosives vest. Earlier, police had said two car bombs were used.
Iraq has been beset with political and sectarian violence for months, often pitting Sunnis -- a minority in Iraq -- against Shiite Muslims, who came to dominate the government after Iraqi leader Saddam Hussein was overthrown in 2003.
Violence has escalated over the past year. The United Nations said 2013 was the deadliest year in Iraq since 2008, with more than 8,800 people killed, most of them civilians.
The army and police will cast their ballots Monday in the parliamentary elections. The general public will vote Wednesday.
Some 277 political entities across Iraq will compete for 328 seats of the Iraqi Council of Representatives, the country's parliament. There are 9,032 candidates.