Arab Gulf nations view Iran as a regional menace and have long accused it of meddling in other countries' affairs.
Iran's president on Sunday accused an unnamed US -allied country in the Persian Gulf of being behind a terror attack on a military parade that killed 25 people and wounded 60, further raising regional tensions.
The spokesperson described falsely the writer as a "political advisor".
The anti-government Arab group - Ahvaz National Resistance - and ISIS both said they had committed the brutal killings.
However, Emirati academic Abdulkhaleq Abdulla, has tweeted on the Ahwaz attack by saying: "A military attack against a military target is not a terror act".
Speaking at a military rally in Tehran, he said Trump will fail in the "economic and psychological war" he's launched against Iran, just as Hussein failed in his war against the Islamic Republic.
Ahvaz lies in Khuzestan, a province bordering Iraq that has a large ethnic Arab community and has seen separatist violence in the past that Iran has blamed on its regional rivals.
The Guard said in its statement that it was willing to pursue the attackers "regionally and beyond".
There was no immediate Gulf Arab comment on his remarks.
The shooting attack on the military parade in the southwestern city of Ahvaz was one of the worst ever against the Guards - Iran's most powerful military force - and is bound to ratchet up tensions with Saudi Arabia. "The attack will strengthen the IRGC's position inside Iran and in the region", Tehran-based political analyst Hamid Farahvashian said.
Kavanaugh accuser looks to negotiate conditions to testify later next week
In a recent interview , Ford claimed that Mark Judge, a close friend of Kavanaugh's, was an eye witness to the sexual assault. However, Prof Ford has set out conditions for her appearance which have yet to be agreed by the Senate Judiciary Committee.
Abolfazl Shekarchi, a senior spokesman for the Iranian military, said "terrorists" behind the Ahvaz attack were not members of IS or groups opposed to the Islamic establishment.
The Afghan government on Sunday strongly condemned the deadly attack by gunmen on a military parade in Ahvaz city inIran on Saturday that killed 29 people and wounded almost 70 others.
Tehran has made no secret of its mounting fury at the U.S. over tightening sanctions, with Javad Zarif, the foreign minister, taking to Twitter on Friday to denounce "the Trump administration's sense of entitlement to destabilise the world along with rogue accomplices in our region".
But in a statement on its website, the group denied any involvement, accusing Iranian authorities of ordering the attack to distract from Tehran's support for "militias in the region".
In 2015, under then-President Barack Obama, the U.S. and Iran reached a landmark nuclear deal - also signed by China, Russia, the UK, France and Germany - where Iran limited its nuclear activities in exchange for sanctions relief.
Britain said its diplomat had extended the country's condolences to Tehran and that Iranian officials were planning to lodge a formal complaint with the United Kingdom's media watchdog, Ofcom.
"It is not acceptable that these groups are not listed as terrorist organisations by the European Union as long as they have not carried out a terrorist attack in Europe", foreign ministry spokesman Bahram Qasemi was quoted as saying by IRNA.
Speaking in NY on Saturday, his personal lawyer Rudy Giuliani claimed that U.S. sanctions were working in Iran and that the coercive measures could lead to a "successful revolution".
The attack took place Saturday at an annual event in Ahvaz, killing at least 29 people, including several civilians, and injuring almost 70 others.