A statement from the intelligence ministry, published by state media, said "the main elements behind the killings... were arrested and moved to detention" following an investigation of at least 18 months involving surveillance in Iran and abroad.

It provided no details as to the number of suspects, their identities or nationalities, or when or where they were arrested. But it promised further information would be made public once it was declassified.

The ministry said the suspects were believed to be involved in the murders of Majid Shahriari, a key member of Iran's Atomic Energy Organisation, on November 29, 2010, and Mostafa Ahmadi Roshan, a deputy director of the Natanz nuclear enrichment facility, and his bodyguard on January 11, 2012.

Those men were killed when unidentified assailants on motorbikes attached limpet-style bombs to their cars in peak-hour Tehran traffic.

Iranian officials have previously blamed the Israeli and US intelligence services for those and two other murders of Iranian scientists carried out since 2010.

Israel has neither confirmed nor denied involvement in the killings. Washington strongly denied complicity in assassinating Roshan.

Iran last month hanged an Iranian man, Majid Jamali Fashi, convicted of being a "Mossad spy" and the killer of nuclear scientist Masoud Ali Mohammadi, who died in a bomb attack outside his home in January 2010.

Tehran from time to time announces the arrest of suspected Israeli or US spies, but provides little or no public evidence supporting the accusations.