Iran has accused United States-backed Gulf states of being behind an attack on Saturday that killed at least 25 people and wounded more than 60 in the deadliest terror attack to strike the country in nearly a decade.
Militants disguised as soldiers opened fire on an annual Iranian military parade in the country's oil-rich southwest. Women and children scattered with Revolutionary Guard soldiers as heavy gunfire rang out at the parade in Ahvaz, the chaos captured live on state television.
The region's Arab separatists, once known only for night-time attacks on unguarded oil pipelines, claimed responsibility for the assault and Iranian officials appeared to believe the claim. Iran summoned diplomats from Britain, Denmark and the Netherlands yesterday for allegedly harbouring "members of the terrorist group" that launched the attack.
Iranian Foreign Minister Mohammad Javad Zarif blamed regional countries and their "US masters" for funding and arming the separatists.
"Iran will respond swiftly and decisively in defence of Iranian lives," Zarif wrote on Twitter.
The attack came as rows of Revolutionary Guardsmen marched down Ahvaz's Quds, or Jerusalem, Boulevard. It was one of many parades around the country marking the start of Iran's long 1980s war with Iraq.
Journalists and onlookers turned to look toward the first shots, then the rows of marchers broke as soldiers and civilians sought cover under sustained gunfire. Iranian soldiers used their bodies at times to shield civilians, with one Guardsman in full dress uniform and sash carrying away a bloodied boy.
"Oh God! Go, go, go! Lie down! Lie down!" one man screamed as a woman fled with her baby.
In the aftermath, paramedics tended to the wounded as soldiers, some bloodied, helped their comrades to ambulances.
State-run IRNA news agency said the gunmen wore military uniforms and targeted a riser where military and police commanders were sitting. At least eight of the dead served in the Revolutionary Guard, an elite paramilitary unit that answers only to Iran's supreme leader.
President Hassan Rouhani ordered Iran's Intelligence Ministry to immediately investigate the attack.
Supreme Leader Ayatollah Ali Khamenei described the attack as exposing "the atrocity and viciousness of the enemies of the Iranian nation". "Their crime is a continuation of the conspiracies by the US-backed regimes in the region which have aimed at creating insecurity in our dear country," Khamenei said in a statement. "However, to their dismay, the Iranian nation will persist on the noble and prideful path they have taken and will - like before - overcome all animosities."
Tensions have been on the rise between Iran and the US. The Trump Administration in May pulled out of the 2015 nuclear accord with Iran, and since then has reimposed sanctions that were eased under the deal. It also has steadily ramped up pressure on Iran to try to get it to stop what Washington calls "malign activities" in the region.
Initially, authorities described the assailants as "takfiri gunmen", a term previously used to describe Isis (Islamic State). Iran has been deeply involved in the fight against Isis in Iraq and has aided embattled Syrian President Bashar al-Assad in his country's long war.
But later, state media and government officials seemed to come to the consensus that Arab separatists in the region were responsible. The separatists accuse Iran's Persian-dominated Government of discriminating against its ethnic Arab minority.
Iran has blamed its Mideast archrival Saudi Arabia for funding Arab separatists' activity. State media in Saudi Arabia did not immediately acknowledge the attack.
Isis claimed responsibility but provided no evidence.