US ambassador to the UN, Nikki Haley has urged Iran to "look in the mirror" for the causes of an attack on a military parade that killed at least 29 people on Saturday.
Haley said Iranian President Hassan Rouhani had "oppressed his people for a long time", BBC reported on Sunday.
She was responding to Rouhani's fierce criticism of the US, in which he blamed it for enabling the attack.
Two separate groups have claimed they carried out the shooting, but neither has provided evidence.
Four gunmen opened fire at Revolutionary Guard troops in the south-western city of Ahvaz on Saturday, killing 29 people people including soldiers and civilians watching a commemorative parade.
One of the victims was a four-year-old girl.
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An anti-government Arab group -- Ahvaz National Resistance -- and the Islamic State (IS) group both claimed responsibility for the killings.
A video released by the Islamic State group's news agency, Amaq, shows three men in a car who appear to be dressed in Islamic Revolutionary Guards Corps (IRGC) uniforms, possibly on their way to carry out the shooting.
The men do not identify themselves as members of IS in the video, but do talk about the importance of jihad.
Rouhani said the "bully" US, along with Gulf states it backed, had enabled the attack.
But the US has denied responsibility and says it condemns "any terrorist attack", while a senior official for the United Arab Emirates - one of the countries Rouhani was thought to be referring to - called the accusations "baseless".
"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," Haley told CNN.
"He can blame us all he wants. The thing he's got to do is look in the mirror."
Rouhani will face US President Donald Trump at the UN General Assembly this week.
Speaking on Sunday, before leaving for the UN in New York, Rouhani vowed that Iran would "not let this crime stand".
"It is absolutely clear to us who committed this crime... and whom they are linked to," he said.
He alleged that a Gulf country had supported the "financial, weaponry and political needs" of the attackers.
He added: "The small puppet countries in the region are backed by America, and the US is provoking them and giving them the necessary capabilities."
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