Iranian officials on Sunday ruled out that the explosion in the southern city of Shiraz that claimed 11 lives was an attack, saying instead it was an incident that was likely caused by leftover ammunition. The explosion had ripped through a mosque packed with hundreds of worshippers in Shiraz late Saturday. It went off as a cleric was delivering his weekly speech against extremist Wahabi beliefs and the outlawed Bahai faith, the semiofficial Fars news agency said. Authorities said 191 people were also wounded, some of them critically, the state IRNA news agency reported. On Sunday, deputy interior minister in charge of security, Abbas Mohataj, said the explosion was "the result of an incident." He didn't elaborate. The police chief of the southern Fars Province, Gen. Ali Moayyedi, said he "rejects" the possibility of an intentional bombing and "any sort of insurgency" in the blast. Moayyedi, in comments carried by state IRNA news agency, said the initial investigation found remnants of ammunition from a military exhibition that was held recently at the mosque. Meanwhile, Iranian foreign ministry spokesman, Mohammad Ali Hosseini said Sunday that no group has yet claimed responsibility for the explosion. A witness to the blast, Mostafa Nazari, told The Associated Press that some 1,000 worshippers had gathered at the mosque grounds to hear a cleric speak. He said it was fortunate the blast happened at a part of the building far from the podium, around which most of the audience had crowded. "Otherwise it would have caused more casualties," Nazari said. The explosion shook houses more than 2 kilometers (a mile) away. Ambulances and firefighters rushed to the scene but a stampede by the crowd made their work more difficult, Nazari added. Early on, the Fars agency quoted a local police official as saying a homemade bomb had caused the explosion and indicated the attack could been religiously motivated. But the agency backed off those speculations on Sunday. Shiraz, some 700 kilometers (440 miles) south of Tehran and the capital of Fars province, is a major draw for foreign tourists who come to see the ruins of nearby Persepolis, the capital of ancient Persia. The blast was a rare incident in the otherwise peaceful town, and officials urged the public to donate blood and called all nurses in the city in on duty. Iran is predominantly Shiite Persian but has faced several deadly attacks in recent years said to have ethnic and religious motivation - though none have seriously threatened the government. In February 2007, a car loaded with explosives detonated by a bus with members of Iran's Revolutionary Guard, killing 11 of them and wounding more than 30 in southeastern Iran. A Sunni militant group, Jundallah or God's Brigade, seen linked to al-Qaida, claimed responsibility at the time. Besides the violence in the southeast, ethnic Arab Sunni militants have been blamed for bombings in the western city of Ahvaz near the border of Iraq _ including blasts in 2006 that killed nine people. The fundamentalist Wahabi strain of Islam considers Shiites heretics. Wahabis are suspected of having influence over some militants in Iraq. The Bahai faith, which claims its founder was a new prophet in the series that included Moses, Jesus and Muhammad, was banned after the 1979 Islamic revolution in Iran.