Iran's intelligence minister says authorities have arrested members of a group which allegedly carried out an attack in northwestern Iran on Wednesday that killed 12 people.
Heidar Moslehi did not publicly identify the group Thursday.
However, he said those responsible for what he called "this terrorist attack" had targeted "unity" between Shi'ites and Sunnis in the region.
The bombing in the town of Mahabad came during a military parade marking the 30th anniversary of the start of the Iran-Iraq War. Officials say at least 70 others were injured in the blast.
No group has claimed responsibility. Local officials blamed Kurdish separatists. But a leading Kurdish faction condemned the bombing.
Some information for this report was provided by AP and Reuters.