TEHRAN : Police in Iran killed four Islamic State suspects, two of them foreigners, in the southern province of Hormuzgan and seized explosives, guns and the group's flag, an Iranian news agency said on Monday.

A major security operation is underway after 17 people were killed last Wednesday in suicide bombings and gun attacks in Tehran, the first to be claimed by the hardline group Islamic State inside Iran.

"Police forces clashed with the four men and killed them in a mountainous area in southern Iran," the semi-official Tasnim news agency quoted a local police chief as saying.

Two of those killed were not Iranian, he said, without elaborating.

Guns, ammunition, explosives and the flag of Islamic State were seized during the operation, Tasnim reported, citing the police chief.

A local official at the port town of Jask, also in Hormuzgan, said five suspects linked to Islamic State were detained on Monday, Iran's Mizan news agency reported.

Southern Iran is home to a minority and has seen previous clashes between security forces and insurgent groups.

The authorities say Iranian security forces killed the mastermind of the attacks on Saturday and that more than 50 suspects have been arrested around the country.

Iran accuses Saudi Arabia of funding hardline militants, including Islamic State, and in the wake of last week's attack pointed the finger at its regional rival. Riyadh has denied involvement in the attacks.