The exchange follows threats from Iran's Revolutionary Guards to avenge the assault on a military parade. Iran-US ties have worsened after President Donald Trump renewed sanctions on Tehran over its nuclear program.
Iranian President Hassan Rouhani on Sunday blamed the United States for instigating its allies in the Middle East to carry out the attack on an annual military parade in the city of Ahvaz.
Rouhani's charge came as Tehran summoned diplomats from Britain, Denmark and the Netherlands, who it accused for harboring members of the al-Ahvazieh militant group, which claimed responsibility for Saturday's attack that killed 25 people and injured dozens more.
"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 before leaving for the UN General Assembly in New York.
Rouhani did not name the "mercenary" US allies, but he could be referring to regional foe Saudi Arabia, and the United Arab Emirates and Bahrain.
Iran has previously blamed Saudi Arabia for supporting Arab separatists in the Islamic Republic. Both countries have been vying for predominance in the region for decades, supporting opposing sides in the civil wars in Yemen and Syria.
The UAE, whose envoy was also summoned by the Iranian Foreign Ministry, denied the allegations.
The "formal incitement against the UAE from within Iran is unfortunate, and has escalated after the Ahvaz attack," Minister of State for Foreign Affairs Anwar Gargash said in a tweet.
'Look in the mirror'
Nikki Haley, US ambassador to the United Nations, rejected Rouhani's accusations.
"He's 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 that's coming from," she told CNN. "He can blame us all he wants. The thing he's got to do is look in the mirror."
Ties between Iran and the US have worsened after President Donald Trump abandoned the multilateral Iran nuclear agreement and renewed sanctions on Tehran.
'Deadly and unforgettable revenge'
Iran's elite Revolutionary Guards (the IRGC) vowed to exact "deadly and unforgettable" vengeance for the attack — one of the worst of its kind against the most powerful force of the Islamic Republic — that killed 12 of their members.
"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," the IRGC said in a statement carried by state media.
Four gunmen in military uniforms fired on a viewing stand in the southwestern city of Ahvaz where Iranian officials had gathered to watch the annual parade. Women and children fled for their lives, along with soldiers, as gunfire crackled.
The self-styled "Islamic State" has also claimed responsibility for the attack, but like the other militant group, it did not provide any evidence.
ap/msh (AP, Reuters)