The self-styled "Islamic State" has also claimed responsibility for the attack but like the other militant group, it did not provide any evidence.
"All these little mercenary countries we see in this region are backed by America".
Iran's Foreign Minister Mohammad Javad Zarif also tweeted that "Iran will respond swiftly and decisively in defense of Iranian lives".
They are divided over whether they want independence or devolution of power within a democratic, federal Iran, but at their most ambitious, some Ahvazi groups want an independent state stretching beyond the borders of Khuzestan, which sits at the head of the strategic Gulf waterway and shares a border with Iraq.
President Donald Trump's decision to withdraw the United States from an worldwide nuclear deal from Iran will also give hardliners more political leverage because they argued that the United States should not be trusted.
Iran's Revolutionary Guard vowed "deadly and unforgettable" vengeance yesterday (Sunday) for the mass shooting at a military parade as Iran's president blamed USA -backed insurgents for killing 25 people in a hail of bullets. If they can trap the United States into doubling down on its military presence in the Middle East, however, then they can use American power to balance Iran.
But US envoy to the UN, Nikki Haley, has implored Iran to "look in the mirror" for causes of the attack before it blames the US.
In its annual Country Reports on Terrorism released on September 19, the State Department claimed that Iran remains the world's leading state sponsor of terrorism and is responsible for intensifying multiple conflicts and undermining U.S. interests in Syria, Yemen, Iraq, Bahrain, Afghanistan, and Lebanon.
This is the shocking moment gunmen disguised as soldiers opened fire at an annual Iranian military parade, killing at least 25 people and injuring 53.
Elsewhere in his remarks, Rouhani hit out at the United States for abusing the UN which Trump reportedly plans to use for a series of speeches to push a hard line against Iran.
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State-run news agency IRNA reported gunmen were dressed in guard uniforms and targeted a platform where military and police commanders were sitting. "The fact that they are angry at our missiles shows that these are the most influential weapons Iran has". We've called them out for their support of terrorism.
Why does Iran blame its Gulf neighbours for the attack?
Hezbollah in a statement said "satanic and malignant hands are behind this terrorist action", and accused the United States and its allies of conducting it "directly or by proxy".
Iran's Foreign Ministry summoned the ambassadors of the Netherlands and Denmark, along with a senior British diplomat, on Saturday to issue a strong protest, Iran's state-run media reported.
Hassan Rouhani's comments came as Iran's Foreign Ministry also summoned Western diplomats over them allegedly providing havens for the Arab separatists who claimed Saturday's attacks in the southwestern city of Ahvaz.
"It is not acceptable that these groups are not listed as terrorist organizations by the European Union as long as they have not carried out a terrorist attack in Europe", Qasemi was quoted as saying by IRNA news agency.
The Iraqi border crossing authority said Saturday that the Iranian side was temporarily closing al-Sheeb and al-Shalamcha crossings between the two countries after the attack.
However, Iranian officials have seized on the fact the separatists immediately made their claim of responsibility on a Saudi-linked, Farsi-language satellite news channel based in Britain.
There has been a blizzard of furious statements from top Iranian officials, including President Hassan Rouhani, accusing Iran's adversaries the United States and Gulf kingdoms of provoking the bloodshed and threatening a tough response. The U.A.E is a Saudi ally, and hosts a significant USA military presence.