A suicide bomber killed 29 people in Baghdad Sunday night.
Authorities said the bomber disguised himself as a beggar and attended prayers at the Um al-Qura mosque in western Baghdad for almost a week before he carried out the attack.
Guards first became suspicious when they saw the man moving through the crowd trying to get close to Sheik Ahmed Abdul Gafur al-Samarraie, head of an endowment that oversees all Sunni religious sites nationwide. They took the man outside, but he returned through a back door and blew himself up when he was a few steps away from al-Samarraie.
No group has claimed responsibility for the bombing, but suicide attacks generally are a hallmark of al Qaeda.
On Baghdad's streets, weeping relatives and friends held funeral processions for the slain worshippers.
In a statement early Monday, Prime Minister Nouri al-Maliki called on Iraqis to stand strong against terrorists and "pursue them wherever they are."
American troops are set to leave Iraq by Dec. 31.
The Associated Press contributed to this story.