An explosion at a prominent Shia Muslim mosque in the southeast Iranian city of Zahedan killed 30 people and wounded 60 today, the semi-official news agency ILNA reported.
The agency said the blast was a suicide bombing but no person or group had claimed responsibility.
Provincial governor Ali Mohammad Azad was quoted as saying a "terrorist group" had been arrested but only one person was behind the explosion in the city.
"This group intended to use the insecure conditions in Afghanistan and Pakistan as the country prepares to hold its presidential election," he said on the website of state broadcaster IRIB.
"They planned to carry out other terrorist activities in other provinces and regions of the country."
Zahedan is the capital of Sistan-Baluchestan province which shares a border with Pakistan. The province faces serious security problems and there are frequent clashes between police and drug dealers and bandits.
Mr Azad said 15 people were killed and 80 wounded. Other sources gave differing casualty figures.
Iran is preparing for a presidential election on June 12th, in which President Mahmoud Ahmadinejad is seeking a second term and faces three challengers.
Shortly after the explosion, security forces discovered and defused a second bomb near the mosque, the semi-official FARS news agency reported.
Reuters