(Adds quotes, increases number wounded)

TEHRAN, April 12 (Reuters) - A bomb exploded in a mosque in southern Iran on Saturday, killing at least eight people and wounding more than 60 others, Iranian media reported.

Ambulances rushed to the scene of the blast in a crowded district in the city of Shiraz, state television said.

“The death toll has reached eight and about 66 injured,” the semi-official Fars news agency said, quoting a police official, identified only as General Zamani.

The agency, quoting an unnamed official, said the death toll was expected to rise because some of the wounded were in a critical condition.

The official IRNA news agency said the bomb exploded during an address by a cleric in the Shohada mosque in Shiraz.

Local officials were not immediately available for comment on the blast.

No one has claimed the responsibility for the blast but the deputy governor of the province Mohammad Reza Hadaegh told state television the cause of the blast was under investigation.

Security is normally tight in Iran, where bomb attacks have been rare in recent years. However, in 2005 and 2006, several people were killed in a string of blasts in the southwestern oil city of Ahvaz.

And 65 men were arrested in February and accused of being behind a bombing that killed members of the elite Revolutionary Guards in a southeastern border province. (Additional reporting by Zahra Hosseinian and Hossein Jaseb, Writing by Parisa Hafezi, Editing by Alison Williams)