By Fredrik Dahl
VIENNA, Sept 17 (Reuters) - Power lines to Iran's most controversial nuclear enrichment plant were blown up a month ago, according to its atomic energy chief, who alleged on Monday that the U.N. nuclear watchdog may have been infiltrated by "terrorists and saboteurs".
The accusation coincides with strident Israeli warnings about the need to stem Iran's nuclear programme with a threat of force, as well as new diplomatic efforts to secure better inspections and an abandonment of work that could be used to develop atomic weapons.
The U.N. International Atomic Energy Agency (IAEA) had no immediate response but Fereydoun Abbasi-Davani's comments seemed certain to overshadow those efforts.
He told the IAEA's annual assembly that power lines from the city of Qom to the underground Fordow plant had been blown up on Aug. 17, and "the same act" had been carried out earlier on power lines to Iran's main enrichment plant, near the town of Natanz.
The plants use centrifuges to "enrich" uranium to a higher concentration of the fissile material that be used in nuclear power plans or nuclear weapons.
Fordow worries the West most as it produces uranium of 20 percent fissile purity, more than needed for power plants and only a short technical step from the 90 percent needed for a warhead.
"It should be recalled that power cut-off is one of the ways to break down centrifuge machines," Abbasi-Davani said.
On Aug. 18, he said, an IAEA inspector had asked for an unannounced visit to Fordow, built 80 metres below ground to better protect it against enemy strikes.
"Does this visit have any connection to that detonation? Who, other than the IAEA inspector, can have access to the complex in such a short time to record and report failures?" he asked.
"Terrorists and saboteurs might have intruded the agency and might be making decisions covertly," he said, according to an official Iranian translation of his speech in Farsi.
He later told reporters that back-up power and other defences had prevented any damage to the Fordow plant.
Abbasi-Davani did not say who he believed was behind the attacks, though Iran has often accused Israel and Tehran's Western foes of trying to sabotage its nuclear programme.
At least four scientists associated with the programme have been assassinated since 2010, most recently in January, and the Stuxnet computer virus was used to cause malfunctions in Iran's nuclear enrichment equipment.
But Abbasi-Davani did for the first time explicitly and publicly suggest that the IAEA might be complicit in sabotage.
The IAEA has voiced growing concern about what Western diplomats describe as persistent Iranian stonewalling of its attempts to conduct detailed inspections of Iran's research.
An IAEA report issued late last month did indicate that inspectors had visited Fordow on Aug. 18, but it did not refer to any damage.
Instead it said Iran had doubled the number of centrifuges at Fordow, despite U.N. sanctions, Western attempts to limit Iran's oil exports, and the threat of an Israeli attack.
A Western diplomat said the Iranian allegation that the agency may have been infiltrated by terrorists was "insulting to the IAEA and its professional staff".
"Their (Iran's) assertions are becoming more desperate and ludicrous to distract attention away from their lack of cooperation and duplicity in dealing with the agency," he said.
EU foreign policy chief Catherine Ashton is due to meet Iran's chief nuclear negotiator on Tuesday on behalf of six major powers, and IAEA head Yukiya Amano said on Monday that his agency would hold more talks with Iran about inspections aimed at allaying Western concerns.
Abbasi-Davani, himself wounded in an attack in Tehran two years ago, made clear his view that sabotage would not slow Iran's nuclear programme, which it says is purely peaceful.
Israel, believed to be the Middle East's only nuclear-armed state, sees Iran's atomic work as a threat to its existence and has been suggesting it could launch an attack on Iran to prevent it reaching nuclear weapons capability.
Israeli Prime Minister Benjamin Netanyahu, who has been pressing Washington to threaten military action against Iran's nuclear programme, said on Sunday that Iran would be on the brink of being able to build a nuclear bomb in six or seven months.
The United States and its allies have launched a major naval exercise in the Gulf that they say shows a global will to keep oil shipping lanes open as Israel and Iran trade threats of war.
Abbasi-Davani said Iranian experts had devised "certain ways through which nuclear facilities remain intact under missile attacks and air raids."