The incident occurred as Allawi was leaving the Imam Ali Mosque. Police said a large crowd of worshippers shouted insults at Allawi, and threw objects at him, including shoes -- a grave insult in Iraq.
Allawi's bodyguards reportedly fired into the air to help police disperse the crowd.
The Iraqi National Accord party said Allawi then cut short his visit to Al-Najaf, the holiest Shi'ite city in Iraq, and returned to Baghdad. Allawi, a secular Shi'ite, said in Baghdad that the incident "appeared to be an assassination attempt" against him.