As Iranians held funerals following the Saturday terror attack on a military parade in the southwestern city of Ahvaz, the acting commander of Iran's Revolutionary Guard said that the Islamic Republic would "take revenge" against the United States and "some of its biggest regional allies," according to CBS News.
25 people were killed and at least 60 more wounded in Iran's largest terrorism incident in nearly a decade. Nearly half of the dead are members of the Revolutionary Guard.
Speaking at the funeral ceremony, acting commander Hossein Salami vowed to strike back against the "triangle" of Saudi Arabia, Israel and the United States.
"You are responsible for these actions; you will face the repercussions," said Salami. "We warn all of those behind the story, we will take revenge."
Iranian supreme leader Ayatollah Ali Khamenei warned on Monday that the five attackers were paid by Saudi Arabia and the United Arab Emirates - despite the Islamic State claiming responsibility for the violence - and that Iran would "severely punish" those behind the bloodshed, by which he meant the United States and Israel, who were accused by the deputy head of Iran's Revolutionary Guards as being involved in the attack and said they should expect a "devastating" response from Tehran.
"Based on reports, this cowardly act was done by people who the Americans come to help when they are trapped in Syria and Iraq, and are paid by Saudi Arabia and the UAE," Khamenei said on his official website.
On Monday, thousands of mourners gathered at the Sarallah Mosque on Ahvaz's Taleghani junction, carrying caskets in the sweltering heat.
Others, mainly young people wearing ethnic clothes of the region's Arab minority, held large photographs of those slain in the attack. Of the 25 killed, 12 people were from Ahvaz and the rest from elsewhere in Khuzestan.
The procession walked down the Naderi and Zand Streets, many weeping and beating their chests, a traditional way of showing grief. Mourners played drums, cymbals and horns, according to local custom.
The crowd also chanted slogans of "Death to U.S." and "Death to Israel" - chants staple at Iranian political rallies.
The attack has been claimed by Arab separatists as well as the Islamic State. Five assailants reportedly involved in the attack were all killed as Iranian troops returned fire in the attack and subsequent chase. Meanwhile, the Islamic State posted what they claim is three of its fighters preparing the attack, according to IRNA. Two of the men featured are speaking Arabic with an Iraqi accent according to the New York Times.
On Sunday, Iranian President Hassan Rouhani accused an unnamed US-allied regional country of supporting the attackers - thought likely to be either Saudi Arabia, the UAE or Bahrain - all close US military allies that view Iran as a regional threat for its support for militant groups.
Iran's Foreign Ministry, meanwhile, has summoned Western diplomats and accused them of providing safe havens for the Arab separatists.
"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," Rouhani said in front of the UN General Assembly in New York.
In response, US ambassador to the UN, Nikki Haley, insisted that the Trump administration has no plans for regime change in Iran - telling CNN: "He can blame us all he wants. The thing he's got to do is look in the mirror."
During Monday's funeral ceremonies in Ahvaz, Iranian Intelligence Minister Mahmoud Alavai said that several suspects in the attack have been identified and that "a majority of them were detained."
"We will punish the terrorists, one by one," he promised the mourning families.
Last year, Saudi Arabia's crown prince, Mohammed bin Salman, suggested that it was time to turn external pressure on Iran to internal pressure - and has in repeated interviews likened Iran's supreme leader, Ayatollah Ali Khamenei to Hitler. At one point Salman said "I believe the Iranian supreme leader makes Hitler look good."
Some, such as the secretary of Iran's National Security Council, tried to cool tempers and said Tehran needed to talk to its neighbours to avoid tensions. "It's essential to be fully aware and increase our constructive dialogues to neutralise the plots of enemies who want to create suspicion and disagreement among regional countries," Ali Shamkhani said.
And yet, even he criticized the United States, saying U.S. sanctions against Iran were illegal and that President Donald Trump was using them as a tool for "personal revenge".
Meanwhile, the UAE - a close ally of Saudi Arabia and Washington - rejected Iran's allegations alluding to its involvement in the violence. Commenting on the deadly attack, U.S. Secretary of State Mike Pompeo, when asked by a Fox News interviewer if the United States played any role in the attack, said: "When you have a security incident at home, blaming others is an enormous mistake." He did however say that the loss of innocent lives was tragic, Pompeo added. There has been no reaction yet from Saudi Arabia or Israel.
Iran's accusations of its Gulf neighbors will antagonize Iran's regional foe Saudi Arabia. The oil super-powers are waging a war for influence across the Middle East, backing opposite sides in Syria, Yemen, Iraq and Lebanon, while Saudi Arabia is eager to steal Iran's oil market share as US sanctions force clients to seek oil from other suppliers.
There was a silver lining for the economically embattled ruling regime: analysts said the violence has led to a boost in domestic support for the Guards which they could use to silence their critics, who include pragmatic President Hassan Rouhani.
Rouhani engineered Iran's 2015 nuclear deal with world powers that ushered in a cautious detente with Washington before tensions flared anew with Trump's decision in May to pull out of the accord and reimpose sanctions on Tehran.
Ahvaz National Resistance, an Iranian ethnic Arab opposition movement which seeks a separate state in oil-rich Khuzestan province, and Islamic State have both claimed responsibility. Both were ignored.