(Updates casualty toll, adds witness quotes)
By Zahra Hosseinian and Hossein Jaseb
TEHRAN, April 12 (Reuters) - A bomb exploded in a mosque in the southern Iranian city Shiraz on Saturday, killing at least nine people and wounding more than 100, Iranian media reported.
Ambulances rushed to the scene of the blast in a crowded district of the city, state television said.
"At least nine people were killed and 105 injured in the blast," the semi-official Fars news agency quoting a local hospital official as saying.
The death toll was expected to rise because some of the wounded were in critical condition, the official said.
State television urged people in Shiraz to donate blood for the wounded and said that all nurses in the city had been called to report for work.
The official IRNA news agency said the bomb exploded during an address by a cleric in the Shohada mosque in Shiraz.
Fars said that on Saturday nights the cleric usually gave speeches on the Baha'i faith, an offshoot of Islam considered heretical by the country's Shi'ite Muslim establishment. Its members claim they face discrimination and persecution in Iran.
Iran says that all Iranians, regardless of creed, enjoy the same rights.
No one claimed responsibility for the blast but the deputy governor of the province, Mohammad Reza Hadaegh, told state television an investigation was under way.
Fars quoted a police official as saying the bomb was a "hand-made" device and had been planted in the mosque.
A 20-year-old woman wounded by the blast said there were about 800 people inside the mosque at 1645 GMT, when the bomb exploded. "After we heard an explosion, there was smoke everywhere," Saeedeh Ghorbani told Fars.
Security is normally tight in Iran and bomb attacks have been rare in recent years. Several people were killed in 2005 and 2006 in a string of blasts in the southwestern oil city Ahvaz.
In February, 65 men were arrested and accused of being behind a bombing that killed members of the elite Revolutionary Guards in a southeastern border province which has a minority Arab population.
Tehran has in the past accused Britain and the United States of trying to destabilize the country by supporting ethnic minority rebels operating in sensitive border areas.
Washington accuses Iran of destabilizing Iraq by supporting Iraqi Shi'ite militia groups. Iran denies this.
The United States is leading efforts to isolate Iran over its nuclear programme, which the West fears is a cover for a drive to build nuclear bombs. Tehran says it wants only to generate electricity. (Additional reporting by Zahra Hosseinian and Hossein Jaseb, Writing by Parisa Hafezi, Editing by Tim Pearce)