By Nicholas Vinocur and Fredrik Dahl
PARIS/VIENNA (Reuters) - An exiled opposition group said on Thursday it had obtained information about a secret underground nuclear site under construction in Iran, without specifying what kind of atomic activity it believed would be carried out there.
The dissident National Council of Resistance of Iran (NCRI) exposed Iran's uranium enrichment facility at Natanz and a heavy water facility at Arak in 2002. But analysts say it has a chequered track record and a clear political agenda.
Its new allegation drew a cautious international response: the U.N. nuclear watchdog and France - one of six world powers trying to diplomatically resolve the nuclear dispute with Iran - merely said they would look into the matter.
"We are evaluating this information, as we do with all information relating to the Iranian nuclear program," a French Foreign Ministry spokesperson said.
In Israel, Iran's arch-adversary, an official said: "I have no knowledge of this other than what was reported."
In 2010, when the NCRI said it had evidence of another secret nuclear facility, west of the capital Tehran, U.S. officials said they had known about the site for years and had no reason to believe it was nuclear.
The latest accusation comes less than a month after the election of a relative moderate, Hassan Rouhani, as Iran's new president raised hopes for a resolution of the nuclear dispute with the West, and might be timed to discredit such optimism.
The Islamic Republic says its nuclear energy program is entirely peaceful and rejects U.S. and Israeli accusations that it is really seeking the capability to make nuclear weapons.
But its refusal to curb sensitive nuclear activity, and its lack of full openness with the U.N. nuclear watchdog agency, have drawn tough Western sanctions and a threat of pre-emptive military strikes by Israel.
The Paris-based NCRI said members of its affiliated People's Mujahideen Organisation of Iran (PMOI) inside the country had "obtained reliable information on a new and completely secret site designated for (Iran's) nuclear project".
The NCRI, which seeks an end to Islamist theocratic rule in Iran, is the political wing of the PMOI, which fought alongside Saddam Hussein's forces in the Iran-Iraq war in the 1980s.
The NCRI said the site was inside a complex of tunnels beneath mountains 10 km (6 miles) east of the town of Damavand, itself about 50 km northeast of Tehran. Construction of the first phase began in 2006 and was recently completed, it said.
The group released satellite photographs of what it said was the site. But they did not appear to constitute hard evidence to support the assertion that it was a planned nuclear facility.
A spokesman for the NCRI said he could not say what sort of nuclear work would be conducted there, but that the companies and people involved showed it was a nuclear site. The group named officials it said were in charge of the project.
"Two of the tunnels are about 550 meters (600 yards) in length, and they have a total of six giant halls," it said.
International Atomic Energy Agency spokeswoman Gill Tudor said in Vienna: "The agency will assess the information that has been provided, as we do with any new information we receive."
A Western diplomat accredited to the IAEA told Reuters: "I have heard nothing. My first suspicion is that it is like the 2010 revelation - a tunnel facility the Iranians are keeping quiet, but no known link to the nuclear program."
There was no immediate comment from Iran, which said in late 2009 that it planned to build 10 more uranium enrichment sites on top of its underground Natanz and Fordow plants, but has provided little additional information.
Proliferation expert Mark Hibbs, of the Carnegie Endowment think-tank, said the NCRI report "deserves close attention.
"It has been widely assumed that there is likely some Iranian nuclear infrastructure which is secret, undeclared, and which may be underground," Hibbs said.
Refined uranium can provide fuel for nuclear power plants, which is Iran's stated purpose, but can also be used to make atomic bombs, which the West fears may be the Islamic Republic's ultimate goal.
(Additional reporting by Dan Williams; Editing by Mark Heinrich)