Iranian officials dismissed the possibility of an attack as the cause of an explosion that occurred inside a mosque in Shiraz Saturday, killing 11 people and wounding 191 others.

The blast occurred at 9 p.m. at the Shohada mosque, where about 800 people had gathered to listen to a cleric speaking about the Wahhabi and Bahaism faiths, which are considered heretical by some Shiites.

On Sunday, the deputy interior minister in charge of security, Abbas Mohtaj, said the blast happened accidentally. Iranian police agreed, dismissing the possibility of a planted bomb.

“This may be the result of negligence,” Ali Mohayedi, police chief commander for the Fars province told the Fars news agency. “There had been an exhibition on the Iran-Iraq war in this location. Munitions left may have led to the explosion.”

Mohayedi also said the police had found remnants of ammunition from a military exhibition titled “Sacred Defense” that had been organized at the mosque not long ago.

Investigation is underway, but no terrorist group has yet claimed responsibility for the explosion.

“We cannot make any prejudgments regarding the bomb blasts, and no group has claimed responsibility,” Iran's Foreign Ministry spokesman Mohammad Ali Hosseini said.

He also asked the media not to jump to conclusions before the investigation was ready.

Bombings are quite rare in Iran and the organizers of such attacks have been severely punished when discovered, by the Iranian government.

The Fars news agency, which is semi-official in Iran, first announced the explosion was the result of a bomb attack, but then withdrew the theory.

Shiraz is the fifth biggest city in Iran, with a population of more than one million people. The city is 440 miles south of Tehran and a popular tourist destination, especially for the ruins of Persepolis, the capital of ancient Persia.