The minister said those arrested "were sending information on Iran's nuclear activities abroad", but did not say whom was arrested or when.

"The Monafeqin (hypocrites) played the main role in transferring the information," he said, referring to the People's Mujahedeen, Iran's main armed opposition group that is based in Iraq.

The political wing of the People's Mujahedeen, the National Council of Resistance of Iran, first began disclosing information on the clerical regime's nuclear activities in mid-2002.

Yunessi referred to a series of press conferences held by the group in Washington before the launch of a major probe by the UN nuclear watchdog, the International Atomic Energy Agency (IAEA).

The group had notably revealed the presence of an undeclared enrichment facility at Natanz in the centre of the Islamic republic, alleging the site was part of a nuclear weapons drive.

Iran has since allowed tough IAEA inspections and insists it is merely trying to produce fuel for its atomic energy programme. It denies that it is developing weapons of mass destruction.

IAEA inspections of Natanz revealed traces of highly-enriched uranium -- possibly bomb-grade -- which Iran contends came into the country on equipment bought on the black market.

That question remains one of the main oustanding issues for the IAEA, which is due to hold fresh discussions on Iran beginning September 13.

Yunessi was speaking to reporters during "government week", when ministers habitually give a run-down of their performance in office.

"The department of counter-espionage in the intelligence ministry possesses the most modern technology and controls the infiltration of foreign spying services," he said, adding that in total "tens of spies in all domains" had been picked up.

More recently, the People's Mujahedeen alleged Iran was seeking to cover up a biological weapons plant at Lavizan in Tehran, where it showed satellite images of buildings being razed and topsoil from the site removed.

The IAEA has since inspected the site and the results from soil sample taken there are expected in the coming weeks.

The exiled Iranian opposition has also alleged Iran has a parallel nuclear programme hidden from the IAEA, directly under the supervision of supreme leader Ayatollah Ali Khamenei.

The Iranian press has in recent months reported several cases of alleged military espionage, but Yunessi's comments are the first official confirmation of such arrests.

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