The Iran President has blamed the US and its Gulf allies for an attack on a military parade which killed at least 25 and injured 70 people.
President Hassan Rouhani said an unnamed US-allied country in the Persian Gulf was behind Saturday attack, which was claimed by an Arab separatist group.
Meanwhile, Iran summoned diplomats from Britain, Denmark and the Netherlands early on Sunday for allegedly harbouring "members of the terrorist group" that launched the attack.
Saudi Arabia, the United Arab Emirates and Bahrain are all close United Sates military allies that view Iran as a regional problem over its support for militant groups across the Middle East.
Mr Rouhani said: "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."
The attack was the deadliest in Iran for nearly a decade, as militants disguised as soldiers opened fire on an annual military parade.
Iranian foreign minister Mohammad Javad Zarif earlier blamed regional countries and their "US masters" for funding and arming the separatists, as regional tensions remain high after the US withdrawal from the Iranian nuclear deal.
The attack killed at least 25 people and wounded around 70, according to the state-run IRNA news agency.
At least eight of the dead served in the Revolutionary Guard, an elite paramilitary unit that answers only to Iran's supreme leader, according to the semi-official Tasnim news agency. State TV hours later reported that all four gunmen had been killed.