A suicide attack has killed at least 38 people and wounded more than 60 others near a mosque in the southeastern Iranian city of Chabahar as Shias marked the climax of Ashoura.
The ritual commemorates the seventh century death of Prophet Mohammed's grandson, Hussein.
Alireza Ronaghi, Al Jazeera's correspondent in Tehran, said that the governor of Chabahar, Seyyed Ali Baateni, confirmed Wednesday's attack saying that there had been "two suicide bombers, one of whom has been arrested. The other detonated his explosive vest before being arrested".
"Baateni says there has been only one explosion, two bombers and anything other than this is denied," our correspondent said.
"But I think the death toll may rise."
The area where the attack took place is home to an armed Sunni group, Jundallah, or Soldiers of God, which has waged sporadic attacks to fight alleged discrimination against the area's Sunni minority in overwhelmingly Shia Iran.
There was no immediate claim of responsibility, but the use of multiple suicide attackers to target Shia worshippers is a tactic the group has employed in the past.
Mahmoud Mozaffar, a senior Iranian Red Crescent Society official, said emergency services had been put on alert over the past few days because of anonymous threats, according to the news agency, ISNA.
Unlike most of Iran, Sistan-Baluchestan has a significant Sunni community and has seen persistent unrest in recent years by the Sunni militant group Jundallah.
Source: Al Jazeera.