TEHRAN An explosion at a prominent Shi'ite Muslim mosque in the southeast Iranian city of Zahedan on Thursday killed 30 people and wounded 60, 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.
Azad said 15 people were killed and 80 wounded. Other sources gave differing casualty figures.
Iran is preparing for a presidential election on June 12, 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.
The attack was carried out on a public holiday for Shi'ite Muslims. Zahedan is a mostly Sunni city.
Earlier, Azad told state television the explosion occurred at about 7:45 p.m. (1515 GMT) when many people were inside the Ali Ebne-Abitaleb mosque for prayers.
A bomb attack in Zahedan in February 2007 which killed 18 Revolutionary Guards was claimed by Jundallah, an insurgent group that says it is fighting for the rights of Iran's Sunni Muslim minority.
The presidents of Iran, Pakistan and Afghanistan met in the capital Tehran for their first summit on Sunday, in an effort to improve cooperation in fighting terrorism and drug trafficking and tackling other regional security problems.
Pakistan and Afghanistan are battling to stem the spread of Taliban insurgencies in their countries, and Iran and Pakistan want a stable Afghanistan because the drugs trade has had a dire effect on Iran and past Afghan violence sent millions of refugees across the border.
(Additional reporting by Hossein Jasseb, editing by Tim Pearce and Andrew Dobbie)