Iran's intelligence chief has accused the UN nuclear watchdog agency of sending spies in the guise of inspectors to gather information about the country's nuclear activities, state TV reported.
The claim was another sign that Iran has hardened its stance since the assassination a week ago of a prominent nuclear scientist and the wounding of another.
Iran is to hold talks in Geneva on Monday and Tuesday with world powers trying to persuade it to curtail key elements of its nuclear work.
Intelligence Minister Heidar Moslehi said staff sent by the International Atomic Energy Agency had engaged in espionage and the Vienna-based agency must take responsibility for their actions. He did not elaborate or identify the inspectors Iran was accusing.
Iran has increasingly complained in recent months about the leaking of information gathered by the agency's inspectors to US officials and other allies.
"Among the individuals the IAEA sends as so-called inspectors, there are spies from intelligence services. The IAEA must be held responsible for this," state TV quoted Mr Moslehi as saying.
Iran said Monday's killing of nuclear scientist Majid Shahriari in a bomb attack and the wounding of another scientist in a separate attack in Tehran was part of a Western campaign to sabotage its nuclear programme.
According to Iran, that campaign has included the abduction of Iranian scientists, the sale of faulty equipment and the planting of a destructive computer worm known as Stuxnet, which briefly brought Iran's uranium enrichment activity to a halt last month.
Iran's chief suspect is arch enemy Israel, whose Mossad spy agency has a long history of assassinating foes far beyond the country's borders.
Mr Moslehi again accused Israel's Mossad, Britain's MI6 and the CIA of being behind the attacks.