The International Atomic Energy Agency is investigating whether Iran hacked into its inspectors' computers and telephones, according to reports heard by senior Western diplomats.
One diplomat in Vienna said he believed a media story of possible hacking was true and that it would be "a dramatic and troubling indication of Iranian disdain for its obligation to cooperate with the IAEA".
Another diplomat said: "I had heard that there had been some sort of interference in this kind of way with laptops and/or mobile phones and so on."
The Wall Street Journal reported on Thursday that the UN nuclear watchdog was investigating whether Iran had succeeded in hacking into computers and telephones carried by IAEA inspectors while they were visiting nuclear facilities in Iran.
It quoted diplomats as saying that, while it was unclear if Iran had succeeded in gaining any information, IAEA officials were concerned that it might have read confidential documents that would help it to identify and potentially punish people assisting the inspectors, or to evade the agency's probes.
IAEA director general Yukiya Amano, asked at a news conference in Brussels if he could confirm the reports, said: "For the specific question that you ask me, I am not in a position to discuss it right now ...
"In general, the IAEA inspections should be done without any disturbance from the country that receives inspectors. We should be able to inspect everything under the safeguards without disturbance."
Iranian officials were not immediately available for comment.
The Journal said the IAEA investigation focused on whether inspectors' telephone SIM cards, or other components, had been manipulated or replaced to allow conversations to be monitored.
If the incident is confirmed, a Vienna-based diplomatic source said it would directly contradict Iran's assertion that it was cooperating with the agency's work.
The IAEA has been investigating Western intelligence reports indicating that Iran has coordinated efforts to process uranium, test explosives at high altitude and revamp a ballistic missile cone to take a nuclear warhead. IAEA inspectors visit Iran regularly to monitor its atomic activities.
Iran denies Western accusations that it is seeking a nuclear weapons capability, saying its atomic activities are aimed at generating electricity so it can export more of its oil and gas.
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