Iranian security forces arrested suspects behind a bomb explosion at a mosque in the southeastern Iranian city of Zahedan on Thursday that left 15 people dead, state-run television IRIB reported.
"A bomb explosion at the 'Amir Al-Momenin' mosque in Zahedan left 15 people killed and 80 others wounded," Governor Ali-Mohammad Azad was quoted as saying by IRIB in its website.
"Security forces arrested suspects behind the bombing," said the governor without elaborating.
Security forces also found and defused another bomb located near the mosque shortly after the blast, the Fars reported news agency.
FARS also reported a higher toll as 20 and said the explosion was a suicide bombing, a claim which has not been officially confirmed.
The explosion caused some damage to the mosque, which is the second biggest Shia mosque in the city. It was packed with worshippers at the time of evening prayers on the occasion of a Shia mourning anniversary.
Zahedan is the capital of Sistan-Baluchestan province, where Iranian security forces often clash with armed bandits and drug-smugglers.
Bordering Afghanistan and Pakistan, Sistan-Baluchestan is not only a major transit route for narcotics but also has been hit by a string of attacks and kidnappings blamed on the radical Sunni group of Jundullah (Allah's Brigade).
The last major attack by Jundullah was February 2007 when a car bomb went off in Zahedan and hit a bus belonging to the paramilitary revolutionary guards (IRGC). Most of the 11 fatal victims belonged to the administrative staff of the IRGC.
Iran accuses Jundullah - and the US and Britain - of sowing discord between Shia, which form the majority of Iranian Muslims and the Sunni minority living mainly in the southeastern and southwestern provinces of Iran.
Iran is preparing for the June 12 presidential election, in which President Mahmoud Ahmadinejad - seeking a second term - and his three challengers started their 20-day campaigning since Friday.