The UN atomic agency and a US research group said Wednesday that they had no indications that an explosion took place at an Iranian nuclear facility, as reported by Israeli and US media.
"We understand that Iran has denied that there has been an incident at Fordo. This is consistent with our observations," said Gill Tudor, spokeswoman for the International Atomic Energy Agency.
The reports cited the conservative American news website WND, which said an explosion at the Fordo facility on January 21 had caused major damage and trapped workers.
Iran denied any such blast took place, with a senior lawmaker calling the rumours "Western propaganda" aimed at influencing upcoming talks with world powers on Iran's nuclear programme.
In Washington, the Institute for Science and International Security, which has voiced concern about Iran's nuclear activities, also cast doubt on the report of an explosion.
The private research group said that a commercial satellite image taken a day after the purported explosion showed no outward signs of damage to the Fordo site.
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"Although an underground explosion may not leave visible exterior signs of damage, ISIS observed no intensified activity in the form of emergency or cleanup vehicles that one would expect to see around the site in the wake of an incident of this magnitude," it said in a statement.
Fordo, dug into a mountain near the holy city of Qom, some 150 kilometres (90 miles) south of Tehran, is at the heart of international concerns over Iran's nuclear drive.
The site, whose existence was revealed in 2009, began in late 2011 to enrich uranium to purities of 20 percent, close to the 90-percent level needed for a nuclear weapon.
Iran says it is enriching to this level to provide fuel for the Tehran Research Reactor, which produces medical isotopes, and denies seeking or ever having sought nuclear weapons.
Iran has accused the United States and Israel of being behind the assassinations of nuclear scientists and sabotage attempts, including the Stuxnet computer virus.
Closing Fordo was a key demand by six world powers -- permanent UN Security Council members Britain, China, France, Russia and the United States plus Germany -- in a series of meetings last year. A new meeting is expected soon but no date or venue has been set yet.