The attack took place outside the Imam Hussein Mosque in the port city of Chahbahar, near the border with Pakistan, the official IRNA news agency said.

The bombers targeted a group of worshippers at a mourning ceremony a day before Ashoura, which commemorates the seventh century death of the Prophet Muhammad's grandson Hussein, one of Shiite Islam's most beloved saints.

Southeastern Iran is home to an armed Sunni militant group, Jundallah, or Soldiers of God, which has waged sporadic attacks to fight alleged discrimination against the area's Sunni minority in overwhelmingly Shiite Iran.

There was no immediate claim of responsibility, but the use of multiple suicide attackers to target Shiite worshippers is a tactic the group has employed in the past.

AP