A shooting at a military parade on Saturday killed at least 29 people in the southwestern city of Ahvaz in Iran.

The nation’s President, Hassan Rouhani, vowed Tehran’s response to the deadliest attack on Iranian soil for years would be “crushing” while implying the US had a part to play.

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.

Responding to Mr Rouhani’s outspoken censure of the US, in which he accused it of facilitating the attack, Ms Haley told CNN: “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.

“He can blame us all he wants.

“The thing he's got to do is look in the mirror.”

Two groups have claimed responsibility for the Ahvaz attack - but neither has provided any evidence.

The anti-government Arab group - Ahvaz National Resistance - and ISIS both said they had committed the brutal killings.

On Sunday, before a flight to a UN session in New York, Mr Rouhani pledged Iran would “not let this crime stand”.

He said: “It is absolutely clear to us who committed this crime and whom they are linked to.

“The small puppet countries in the region are backed by America, and the US is provoking them and giving them the necessary capabilities.”

Although Mr Rouhani did not mention specifically who the so-called “puppet” nations were, he apparently accused US-backed nations of being complicit in the atrocities.

Mr Rouhani alleged a Gulf state had supported the “financial weaponry and political needs” of the perpetrators.

The comments appear to allude to the alleged involvement of Saudi Arabia, the UAE and Bahrain.