The US ambassador to the UN has urged Iran to “look in the mirror” for the causes of an attack on a military parade that killed 25 on Saturday.
Nikki Haley said Iranian President Hassan Rouhani had “oppressed his people for a long time”.
She was responding to Mr 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 25 people including soldiers and civilians watching a commemorative parade.
One of the victims was a four-year-old girl.