Revolutionary Guard official's comments come after Iranian president blamed US-backed Gulf states for attack on military parade
The deputy head of Iran's Revolutionary Guards warned US and Israeli leaders on Monday to expect a "devastating" response to an attack on a military parade in the city of Ahvaz.
Tehran blames "US-backed regimes in the region" for the attack and sees it as part of a "plot".
"You have seen our revenge before... You will see that our response will be crushing and devastating and you will regret what you have done," Hossein Salami said in a speech before the funeral of the victims broadcast live on the state television.
Thousands of people packed the streets of the southwestern Iranian city of Ahvaz to mourn the victims of Saturday's assault, which killed 25 people, including 12 members of the elite Revolutionary Guards. Many chanted "death to Israel and America".
The coffins, wrapped in the flag of the Islamic Republic, were carried by the mourners. Many held pictures of a four-year-old boy killed in the attack, one of the worst against the most powerful military force of the Islamic Republic.
Iranian women mourn during the funeral on Monday (AFP)
Four assailants fired on a viewing stand in Ahvaz where Iranian officials had gathered to watch an annual event marking the start of the Islamic Republic's 1980-88 war with Iraq. Soldiers crawled on the street to avoid bullets. Women and children fled for their lives.
Salami's comments come a day after Iranian President Hassan Rouhani accused US-backed Gulf states of carrying out the attack.
"America wants to cause chaos and unrest in our country so that it can return to this country, but these are unreal fantasies and they will never achieve their goals," Rouhani said on Sunday.
"The small puppet countries in the region are backed by America, and the United States is provoking them and giving them the necessary capabilities.
"The Persian Gulf states are providing monetary, military and political support for these groups," said Rouhani.
A senior United Arab Emirates (UAE) official denied on Sunday that his country had been involved in the attack.
You will see that our response will be crushing and devastating and you will regret what you have done
- Hossein Salami, deputy head of Iran's Revolutionary Guards
The "formal incitement against the UAE from within Iran is unfortunate, and has escalated after the Ahvaz attack," said Minister of State for Foreign Affairs Anwar Gargash in a tweet.
"The UAE's historical position against terrorism and violence is clear and Tehran's allegations are baseless."
An Iranian ethnic Arab opposition movement called the Ahwaz National Resistance, which seeks a separate state in oil-rich Khuzestan province, claimed responsibility for Saturday's attack.
The Islamic State (IS) group also claimed responsibility, with neither group providing evidence. Later on Sunday, IS' Amaq agency posted a video of three men in a vehicle who it said were on their way to carry out an attack on an Iranian military parade. The video's authenticity has not yet been confirmed.
Iran’s Revolutionary Guards vowed on Sunday to wreak "deadly and unforgettable vengeance" for the attack.
"Considering [the Guards'] full knowledge about the centres of deployment of the criminal terrorists' leaders..., they will face a deadly and unforgettable vengeance in the near future," a statement carried by state media said.
The Iranian president engineered Tehran's 2015 nuclear deal that ushered in a cautious detente with Washington before tensions resurged with President Donald Trump's decision in May to quit the accord and reimpose sanctions.
"America is acting like a bully towards the rest of the world... and thinks it can act based on brute force," said Rouhani on Sunday.
"But our people will resist, and the government is ready to confront America. We will overcome this situation [sanctions], and America will regret choosing the wrong path.
"Iran's answer [to this attack] is forthcoming within the framework of law and our national interests," said Rouhani, adding that the United States would regret its "aggressiveness".
I think the Iranian people have had enough and that's where all of this is coming from
- Nikki Haley, the US ambassador to the United Nations
Rouhani's allegation will likely ratchet up tensions with Iran's rival Saudi Arabia and its Gulf allies, which along with the US have been working to isolate the Islamic Republic.
Despite Iran's comments, Kuwait, Qatar and Oman all condemned the attack on Sunday.
Washington also condemned attack on Sunday but said the country's leaders needed to look at reasons for unrest.
"The United States condemns any terrorist attack anywhere, period. We've always stood by that," Nikki Haley, the US ambassador to the United Nations, told CNN.
But she said of Rouhani: "He's got the Iranian people are 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 that's coming from.
"He can blame us all he wants. The thing he's got to do is look at the mirror."
On Monday, US Defense Secretary Jim Mattis dismissed Iran's threats of revenge and said it was "ludicrous" for Tehran to allege US involvement.
Mattis told reporters at the Pentagon that Iran's threat did not give him any concern.
"We've been very clear that they shouldn't take us on like that. And I am hopeful that cooler, wiser heads will prevail," Mattis said.
"They've so far blamed at least three countries and I think one terrorist group. We'll see how long the list goes. But it'd be good if they knew what they're talking about before they started talking."
There was no immediate comment from Saudi Arabia on Rouhani's allegations.
'Puppets of the United States'
On Saturday, Iranian Supreme Leader Ayatollah Ali Khamenei ordered security forces to bring to justice those responsible for one of the attack.
The Revolutionary Guards are the most powerful military force in the country and answer to Khamenei.
"This crime is a continuation of the plots of the regional states that are puppets of the United States, and their goal is to create insecurity in our dear country," Khamenei said in a statement published on his website.
Women and children died in the assault, in which the four attackers were killed, state news IRNA agency reported.
Women and children died in the assault, in which the four attackers were killed (AFP)
Along with Rouhani and Khamenei, Iranian analysts speaking to Middle East Eye also accused Saudi Arabia of supporting the attack.
Fereidoun Majlesi, a former diplomat and foreign policy expert, told MEE: "I think the proxy war between Saudi Arabia and Iran is entering a dangerous phase.
"The terrorist attack in Ahwaz is probably supported by Saudi Arabia as the officials in Riyadh have already stated that they would take the war inside the Iran soil.
"The Saudis' plan is wrong. They just united Iran. This is the characteristic of Iranians. When people in Iran face a hardship or an attack, they become united to defeat the invaders.
"I strongly believe that such terrorist actions will only increase the nationalism sentiment."
Speaking to MEE, Rasool Hosseini, a reformist foreign policy analyst, said: "I think today's attack is in line with the US and its regional allies' strategy to pressure Iran.
"I should add that the US secretary of state stated yesterday that they would respond to Iran-backed militias' offensive against US interests.
"The attack occurred one day before Rouhani's trip to New York [to attend the United Nations General Assembly].
"I think Rouhani should now use this opportunity to convey this message to the world that Iran is one of the biggest victims of terrorism, while the US labels Tehran as the state sponsor of terrorism."
Attacks on the military are rare in Iran.
Last year, in the first deadly attack claimed by Islamic State in Tehran, 18 people were killed at the parliament and mausoleum of Ayatollah Ruhollah Khomeini, the founder and first leader of the Islamic Republic.