A general view of the attack during the military parade in Ahvaz, Iran September 22, 2018. Tasnim News Agency/via REUTERS

BAGHDAD (Reuters) - Iran’s Revolutionary Guards vowed on Sunday to take “deadly and unforgettable” vengeance against attackers at a military parade who killed 12 of their comrades and 13 others, in a statement carried by Iranian news agencies.

Gunmen who opened fire at a viewing stand in the southwest of the country carried out one of the worst attacks ever against the elite force on Saturday.