Iranian leaders have accused US-backed Gulf states of being behind an attack on a military parade that killed 25 people, including a child.
Supreme Leader Ayatollah Ali Khamenei said “puppets of the US” were trying to “create insecurity” in Iran.
Gunmen opened fire at Revolutionary Guard troops and officials in the south-western city of Ahvaz.
Earlier an anti-government Arab group, Ahvaz National Resistance, and Islamic State (IS) both claimed the attack.
However neither group provided evidence to show they were involved.
Reports say nearly half of those killed were members of the Revolutionary Guard, who are under Mr Khamenei’s command.
Mr Khamenei did not name the “regional states” that he believed were behind the attack.