An Iranian news agency says 20 people have been killed and 55 others wounded in a suicide attack at a Shi'ite mosque in southeastern Iran.
The Fars news agency says Thursday's blast occurred in the mainly Sunni city of Zahedan, the capital of Sistan-Baluchistan province near the Pakistani border.
Provincial governor Ali Mohammad Azad told reporters at least 15 people were killed and another 80 wounded. He said the blast occurred during evening prayer, when several worshippers were inside the mosque.
There has been no immediate claim of responsibility. The provincial governor said a "terrorist" was involved, and that several members of a terrorist group had been arrested, but he did not give details.
In 2007, a bomb attack in Zahedan killed at least 11 members of Iran's elite Revolutionary Guards. The militant group Jundallah, which says it is fighting for the rights of Iran's Sunni minority, claimed responsibility for the attack.
Iranian security forces and drug smugglers also have clashed in the area where the blast occurred.
Campaigning has been under way in Iran in preparation for a presidential election on June 12. President Mahmoud Ahmadinejad is seeking a second term and faces three challengers.
Some information for this report was provided by AFP, AP and Reuters.