Iran says it has killed the alleged mastermind of twin attacks last week claimed by the militant Islamic State (IS) group.

The official IRNA news agency on Sunday quotes Intelligence Minister Mahmoud Alavi as saying the suspect left Iran for a neighboring country following the attacks but "was sent to hell" by Iranian intelligence agents and "fellow intelligence services".

Alavi did not provide further details or offer any evidence.

Five attackers stormed Iran's parliament and a shrine to revolutionary leader Ayatollah Ruhollah Khomeini on Wednesday, setting off clashes with security forces and killing at least 17 people.

Iran says the attackers, who were all killed, had fought for the IS group in Syria and neighboring Iraq. It says dozens of people have been detained.