TEHRAN, Iran - Following one of the worst attacks against Iran's powerful Islamic Revolutionary Guards Corp, the country have vowed to punish those behind the attack.
On Saturday, four assailants opened fire at the country's annual military parade marking the start of the Islamic Republics 1980-88 war with Iraq.
The gunmen opened fire on a viewing stand set up for Iranian officials, who had gathered to mark the event in the country's oil-rich southwestern region.
The attack in Ahvaz city left 25 people dead and nearly 70 others injured.
Half of those killed were members of Iran's powerful security establishment, that has been the sword and shield of Shi'ite clerical rule since Iran's 1979 Islamic Revolution.
The horrific attack was captured on video, which was later distributed to the local media and several others appeared online later.
The videos showed soldiers participating in the parade looking around for the source of the gunshots and then immediately scattering around as the shootout intensified.
In another video, some soldiers were seen ducking and crawling on the ground, while others showed women and children lying in a pool of blood and bloodied soldiers limping toward ambulances. Troops were also seen helping escort women and children to safety amid the gun battle.
Following the attack, Brigadier General Abolfazl Shekarchi, a senior spokesman for Iran's armed forces said, "Three of the terrorists were killed on the spot and a fourth one who was injured died in hospital."
While Iran's state television blamed the attack on Sunni "takfiri terrorists," Ramezan Sharif, a spokesman for Irans Revolutionary Guard Corps blamed minority Arab separatists for the bloodshed.
Iranian Foreign Minister Mohammad Javad Zarif accused, "Terrorists recruited, trained, armed & paid by a foreign regime have attacked Ahvaz."
He said, "Iran holds regional terror sponsors and their U.S. masters accountable for such attacks.
Claiming the bloodshed
Hours after the attack on Saturday, the Ahvaz-based ethnic Arab opposition movement called the 'Patriotic Arab Democratic Movement' or the 'Ahvaz National Resistance' claimed responsibility for the attack.
Iran claims that the group is allegedly supported by "foreign antagonists," including Saudi Arabia.
However, a few hours later the Islamic State Militant Group (ISIS) released a statement on its Amaq News Agency, claiming the attack.
The terror group said that its supporters carried out the killings in Ahvaz.
However, neither the Ahvaz separatist group nor the Islamic State has provided any evidence of their involvement.
Elite forces spokesman Shekarchi, however, argued in an interview with Iran's official IRNA news agency, that the gunmen were trained by two Gulf Arab states and had ties to the U.S. and Israel.
Shekarchi said, "These terrorists... were trained and organized by two ... Gulf countries. They are not from Daesh(Islamic State) or other groups fighting Iran... but they are linked to America and (Israel's intelligence agency) Mossad."
On Sunday, Iranian President Hassan Rouhani alleged that a Persian Gulf country allied with the U.S. was behind the attack.
While Rouhani refrained from naming any country, he said, "All of those small mercenary countries that we see in this region are backed by America. It is Americans who instigate them and provide them with necessary means to commit these crimes."
Earlier in the day, Iran officially summoned diplomats from Britain, Denmark and the Netherlands and accused them of having harboured "members of the terrorist group" that carried out the attack.
According to the semiofficial Iranian Students News Agency, officials in Tehran also summoned the envoy of the United Arab Emirates over irresponsible and insulting statements of an Emirati adviser.
On Sunday, Iran's Tasnim news agency said that at least eight members of the elite paramilitary unit were killed in the attack.
Later in the day, the Revolutionary Guards released a statement, in which they warned that they would seek "deadly and unforgiving revenge."
In a statement featured on state media, the Guards said, "Considering (the Guards) full knowledge about the centers of deployment of the criminal terrorists leaders ..., they will face a deadly and unforgettable vengeance in the near future."
Not only was Saturday's assault, one of the worst ever against the most powerful force of the Islamic Republic, but it was also Iran's deadliest attack in nearly a decade.
The attack comes at a time when the U.S. is strategizing to isolate Iran globally, after walking out of the nuclear deal earlier this year and re-imposing sanctions against the country.
Further, ties between Iran and the U.S. have also been affected due to America's close military ties with its Gulf allies that are Iran's rivals, including the biggest, Saudi Arabia.
However, later in the day, U.S. rejected Iran's accusations, with the U.S. Ambassador to the United Nations, Nikki Haley claiming, "Hes (Rouhani) got the Iranian people ... protesting, every ounce of money that goes into Iran goes into his military, he has oppressed his people for a long time and he needs to look at his own base to figure out where thats coming from. He can blame us all he wants. The thing hes got to do is look in the mirror."