A dissident group, the People's Mujahedeen of Iran, that had previously revealed the existence of several hidden nuclear sites in the country, has claimed that Iran is secretly constructing a vast underground complex to hide a nuclear facility in the mountains east of Tehran, in a development that would violate the UN sanctions regime.

The group has previously revealed secret atomic plants at Natanz and Qom that the Iranian regime has subsequently acknowledged to be nuclear facilities.

The exiled opposition group is a radical but deeply rooted enemy of the Islamic Republic and its armed wing Mujahedeen e-Khalk is proscribed as a terrorist organisation in the US.

"This is certainly part of the secret weapons program. It's just moved underground, in tunnels, hidden from the outside world," The Telegraph quoted Alireza Jafarzadeh, a spokesman for the group who presented photographs of the site in Washington, as saying.

The organisation said it had already provided evidence, including eyewitness reports from inside the facility and satellite images showing considerable development in the remote area, to the United States.

Meanwhile, a Western diplomat said the International Atomic Energy Agency (IAEA), the UN agency that safeguards atomic materials, might examine the report. If the information was credible, the IAEA would demand access to the site to ensure that no refinement of uranium or other nuclear materials had taken place there.

"Any new plant would be in contravention of a six UN security council resolutions warning Iran to suspend all enrichment and reprocessing activities," the diplomat added.

The IAEA released a quarterly report this week on the status of Iran's nuclear program and criticized Tehran for limiting the access of the Agency's inspectors. The report stated that Iran has failed to answer questions concerning its alleged efforts to develop nuclear warheads and triggering devices.

It also claimed that Iran continues to expand its production of nuclear fuel, though not as quickly as some Western intelligence agencies had projected. (ANI)