Explosive blasts destroyed power lines to Iran's underground nuclear facility at Fordo last month, the head of Iran's atomic agency said at a meeting of UN atomic agency member states Monday.
"On ... 17th August 2012, the electric power lines from the city of Qom to the Fordo complex ... were cut using explosives," Fereydoon Abbasi Davani told the 155-nation International Atomic Energy Agency gathering in a speech.
Davani did not accuse anyone of sabotage, but in the past Iran has claimed both Israel and the United States were behind the assassinations of nuclear scientists and computer viruses targetting its facilities.
The day after the power line blasts, "agency inspectors requested to conduct an unannounced inspection. Does this visit have any connection to that detonation?" Abbasi said through an interpreter.
"It should be reminded that the same act had been performed on the power lines to the Natanz facilities."
Fordo is a key site in Iran's nuclear programme, dug deep into a mountain to protect it against air strikes and enriching uranium to purities of 20 percent, a short step from the 90 percent needed for a nuclear weapon.
Iran says its nuclear programme is peaceful and that uranium enrichment is for power generation and medical purposes.
Many in the international community suspect otherwise and the UN Security Council has passed six resolutions calling for a suspension of enrichment and other sensitive activities.
Israel and the US have also refused to rule out military action.