Iranian President Hassan Rouhani vowed on Saturday a "crushing" response to the attack against a military parade in Ahvaz earlier in the day that left 29 people dead. On his Instagram account, Rouhani said “those who are supporting these terrorists will be held responsible.” The attack occurred a day before he heads to New York to address the annual UN General Assembly next week. Supreme leader Ali Khamenei ordered security forces to bring to justice those responsible for one of the worst assaults ever against the Iranian Revolutionary Guards Corps (IRGC), the most powerful military force in the country, which answers to him. Foreign Minister Mohammad Javad Zarif said the attack was carried out by "terrorists recruited, trained, armed & paid by a foreign regime". "Iran holds regional terror sponsors and their US masters accountable for such attacks," he wrote on his Twitter account. The assault, which wounded more than 60 people, targeted a viewing stand where Iranian officials had gathered in the city of Ahvaz to watch an annual event marking the start of Iran’s 1980-88 war with Iraq, state television said. The ISIS terrorist group claimed responsibility for the attack. Russian President Vladimir Putin said he was "appalled by this bloody crime" which was a reminder of the "necessity of an uncompromising battle against terrorism".