Iraqi officials say a double suicide bombing south of Baghdad has killed at least 27 people and wounded more than 100 others.

Al-Qaida in Iraq has claimed responsibility for the attack, which occurred Monday in the town of Hillah.

Officials say two suicide bombers blew themselves up in a crowd of former police commandos who were protesting a decision to disband their unit.

Earlier, the terrorist group said it has launched an offensive to counter a joint U.S.-Iraqi operation aimed at rooting out insurgents from Baghdad.

Iraqi officials have said 40,000 Iraqi troops will take part in the operation, dubbed Operation Lightning. The troops began setting up checkpoints and searching houses around Baghdad on Sunday.

Meanwhile, U.S. forces have released the head of Iraq's top Sunni political party after a brief detention today. The U.S.-led coalition says Mohsen Abdul-Hamid was detained by mistake.

Some information for this report provided by  AFP and Reuters.