Iraqi troops are sealing off Baghdad to search for insurgents in their biggest such operation since the fall of Saddam Hussein.
Iraqi officials say Operation Lighting involves 40,000 Iraqi troops. They began setting up the first of several hundred checkpoints in and around Baghdad Sunday.
Al-Qaida in Iraq says it is launching an offensive to counter the operation. The group also claimed responsibility for Monday's double suicide bombing in Hillah that killed 27 people.
Also Monday, the U.S. military released the head of Iraq's top Sunni political party after mistakenly arresting him hours earlier.
And the U.S. military says an Iraqi aircraft with four Americans and one Iraqi on board crashed in eastern Iraq. The statement says the crash is under investigation and gave no indication whether there are casualties.
Some information for this report provided by AFP, AP and Reuters.