Some others said Wednesday's deadly blast was caused by an explosive devise planted inside the mosque, Aljazeera reported.
The bomb exploded at the entrance of the Shia Muslim mosque where worshippers had gathered for prayers before the breaking of the fast on the first day of Ramadan, AP reported quoting police and hospital officials.
The explosion ripped through strings of light-bulbs and green and red flags hung around the entrance to celebrate the start of the holy month. The mosque's facade was ravaged, shops nearby were detroyed and several cars were damaged.
Hilla, a predominantly Shia town located about 95km south of the Iraqi capital, has been the scene of frequent deadly attacks by anti-government fighters.
Police were trying to determine whether Wednesday's blast was caused by a car packed with explosives or a bomb left at the scene, police spokesman Captain Muthanna Khaled Ali said.
When the blast hit just before 6pm, the faithful had come to the Ibn al-Nama mosque for prayers before returning home to eat the meal that ends the day's sunrise-to-sunset fast, Ali said.
The attack came five days after a car bomb exploded in a crowded Hilla market, killing 10 people, including three women and two children in Hilla.
In other incidents, an Iraqi police officer of the rank of lieutenant-colonel was killed and two other policemen wounded in two separate attacks by armed fighters in the northern Iraqi city of Mosul, Aljazeera reported quoting police sources on Wednesday.
Also, police found the body of an Iraqi who was hanged east of the city.