Iran says it has arrested dozens of people for allegedly spying on the country's nuclear programme.
Iran has been accused of keeping some of its nuclear activities secret
Intelligence Minister Ali Younesi said some of those detained were suspected of passing nuclear secrets to what he termed Iran's enemies.
He said most were linked to the Iranian opposition group based in Iraq, the People's Mujahedin Organisation (MKO).
He blamed the group for leaks about Iran's nuclear activities, currently under investigation by the UN.
Correspondents say tension over Iran's nuclear activities has increased in the run-up to a meeting of the UN's nuclear agency, the International Atomic Energy Agency (IAEA), later this month.
There is no information on when the arrests took place, nor on the nationality of those detained.
Mr Younesi was speaking to reporters during "government week", when ministers habitually give a run-down of their performance in office.
The MKO has in the past made public two undeclared nuclear sites in 2002, alleging they were part of a secret nuclear weapons programme.
One was a large uranium enrichment facility in Natanz, the other a heavy water production facility in Arak.
Alleged military activities
The IAEA is investigating Iran to find out the extent of Iran's nuclear programme and, in particular, whether it is secretly trying to build a nuclear weapon.
In the past it has criticised Iran for not declaring all its activities and it is now checking to see if Iran is complying with the inspection rules.
Washington has accused Tehran outright of attempting to build a nuclear bomb.
Iran says it is attempting to develop a civil nuclear energy programme because its oil reserves are limited.