Iran has put paid to Western spying on its nuclear facilities by ensuring that its physicists and engineers are better looked after, atomic energy chief Ali Akbar Salehi said.

Salehi, who is also a vice president, said that in the past Western countries had lured Iranian nuclear specialists abroad "with offers of better education or jobs outside Iran," the Fars new agency reported on Friday.

"People who fell for it in the past unfortunately leaked information abroad," the news agency quoted him as saying.

"But the (Iranian Atomic Energy) Organisation has been able to gain the trust of its engineers and address their concerns, so they can continue to work in the organisation without any concerns," he added.

Salehi's remarks were not the first admission by Iran of Western or Israeli espionage efforts against its nuclear programme -- it has arrested a number of suspected spies in the past with prosecutors generally seeking the death penalty.

In November 2008, Iran executed telecommunications engineer Ali Ashtiari after he was found guilty of spying for Israel's Mossad spy agency.

Ashtari was convicted of involvement in a Mossad plot to intercept the communications of Iranian military and nuclear officials.

Last week, Intelligence Minister Heydar Moslehi said that authorities had arrested several "nuclear spies" who were working to derail Iran's nuclear programme through cyberspace.

Moslehi's remarks came against the backdrop of reports that the Stuxnet worm was mutating and wreaking havoc on computerised industrial equipment in Iran.

Analysts say Stuxnet may have been designed to target Iranian nuclear facilities, especially the Russian-built power plant in the southern city of Bushehr.

In January 2007, Iran said it had arrested a "spy" working in parliament's research centre on suspicion of passing information on its nuclear programme to the outlawed armed opposition group, the People's Mujahedeen.

In November 2008, the Iranian judiciary cleared ex-nuclear negotiator Hossein Moussavian of spying for the West, despite strong support for the charges from hardline President Mahmoud Ahmadinejad.

Moussavian was spokesman for Iran's nuclear negotiating team under moderate president Mohammad Khatami, Ahmadinejad's predecessor.

Iran's nuclear ambitions are at the heart of a longrunning standoff with the West, which suspects the Islamic republic is seeking to develop atomic weapons under the cover of a civilian drive.

Tehran denies the allegation and is pressing on with its uranium enrichment programme -- the most controversial aspect of its nuclear activities -- despite four sets of UN sanctions.

Salehi said Iran had now ensured that sensitive information about its nuclear programme was not easily accessible.

"In the past, people had easy access to information, but this is no longer true. It is not necessary for everyone to know about everything," he said, adding that Iranian nuclear engineers now enjoyed high-quality housing and education for their children.