The semi-official Fars news agency gave a lower death toll, saying eight people were killed and more than 50 wounded. There was no immediate explanation for the discrepancy.
"As a result of a bomb explosion at Rahpouyan Cultural Center in Shiraz, unfortunately scores of our countrymen were martyred," the state television report said.
The television report said the mosque was part of the cultural center.
Fars said the mosque is the site of weekly speech about extremist Wahabi beliefs and the outlawed Bahai faith.