Ten people died and 57 others were injured when a bomb exploded at military parade in north-western Iran.
The blast in the city of Mahabad, close to the borders with Iraq and Turkey, was blamed on Kurdish separatists who have fought Iranian forces for decades.
Most of the victims were women and children, said provincial governor Vahid Jalalzadeh.
Iranian forces in the border zone have for years clashed with Kurdish rebels from the Iranian wing of the Kurdistan Workers Party, which also has fighters based in Turkey and Iraq. The group in Iran has generally not targeted civilians in its campaign for greater rights for the Kurdish minority, raising the prospect that the bomb might have gone off prematurely.
A state radio report said the device was detonated on a timer and had been placed under a bush near the parade route.
Mr Jalalzadeh said the explosion was carried out by "counter revolutionaries," a reference to the Kurdish separatist group. He called the bombing "a terrorist incident".
The parade was one of several events around the country to mark the 30th anniversary of the start of the Iran-Iraq war. No military personnel were wounded, Mr Jalalzadeh said.
The Mehr news agency said the dead included the wives of two military officers.
"The explosion happened opposite the VIP stage among women who were present there," Mr Jalalzadeh said.
The Iranian branch of the Kurdish rebel group, the Party for Free Life in Kurdistan, says it is fighting for greater rights in Iran.