The explosion hit the Ibn al-Nama mosque, ripping through strings of lightbulbs and green and red flags hung around the entrance to mark the start of the holy month and ravaging the mosque's facade.

Police believed Wednesday's blast was caused by planted explosives, spokesman Capt. Muthanna Khaled Ali said.

When the blast hit just before 6 p.m., 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, adding that at least 22 people were killed and 77 wounded.

The attack came five days after a car bomb exploded in a crowded market, killing 10 people, including three women and two children in Hillah, a Shiite town about 60 miles south of Baghdad that has been the frequent target of attacks.

Wednesday was the first day of the Islamic holy month of Ramadan for Iraq's Shiite majority. Sunnis began marking the month a day earlier.

Al-Qaida in Iraq has called for stepped up attacks during Ramadan.

Thousands of U.S. troops are currently waging two major offensives to try to put down al-Qaida in its strongholds in the mostly Sunni northwest of Iraq.