By Nicholas Vinocur and Fredrik Dahl
PARIS/VIENNA (Reuters) - An exiled Iranian opposition group said on Thursday it had information about what it said was a center for nuclear weaponisation research in Tehran that the government was moving to avoid detection ahead of negotiations with world powers.
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 mixed track record and a clear political agenda.
An accusation it made in July about a secret underground nuclear site under construction in Iran drew a cautious international response, while the United States expressed skepticism about another claim in 2010.
The NCRI's announcement comes days before Iran and six world powers are to meet in Geneva to try to end years of deadlock over the nuclear program, with hopes of a breakthrough raised by the election of a relatively moderate president in Iran, Hassan Rouhani. Iran denies conducting any nuclear weapons work.
The Paris-based NCRI, citing information from sources inside Iran, said a nuclear weaponisation research and planning center it called SPND was being moved to a large, secure site in a defense ministry complex in Tehran about 1.5 km (1 mile) away from its former location.
It said the center employed about 100 researchers, engineers and experts and conducted small-scale experiments with radioactive material.
"There is a link between this transfer and the date of Geneva (talks) because the regime needed to avoid the risk of visits by (U.N. nuclear) inspectors," Mehdi Abrichamtchi, who compiled the NCRI report, told a news conference in Paris.
The International Atomic Energy Agency (IAEA), the U.N. nuclear watchdog, declined to comment.
A Western nuclear expert, Mark Fitzpatrick, said he did not find the NCRI's allegation credible and that U.S. intelligence agencies continued to believe that Iran was "still keeping most of its weaponisation efforts under ice".
"If the NCRI knows about a nuclear weaponisation research and planning center in Iran, you can bet the CIA knows about it too, yet there has been no hint of it in public or leaked assessments," Fitzpatrick, of the International Institute for Strategic Studies, a London-based think tank, told Reuters.
SUSPECTED PROJECT LEADER
The SPND site was mentioned in an IAEA report in late 2011 that included intelligence information indicating past research in Iran that could be relevant for nuclear weapons. Iran dismissed the findings as baseless or forged.
The IAEA document said the information pointed to the existence of a concerted weapons program that was halted in 2003 when Iran came under increased Western pressure. But it suggested that some activities may have resumed later.
The NCRI said such research had continued at several sites, including the SPND. The publication of the IAEA report in 2011 prompted Tehran to start planning for a transfer of its activities to a new site to avoid inspections, it said.
The NCRI, which seeks an end to Islamist theocratic rule in Iran, is the political wing of the People's Mujahideen Organisation of Iran (PMOI), which fought alongside Saddam Hussein's forces in the Iran-Iraq war in the 1980s. The United States last year removed it from its list of terrorist groups.
The NCRI said the SPND's activities had expanded over the past year and a half, under the direction of Mohsen Fakhrizadeh, who was identified in the IAEA report as a key figure in suspected weapons-related work and is subject to U.N. sanctions.
Iranian media rarely mention Fakhrizadeh. Western nuclear experts have said he probably lives under tight security to shield him against assassins and keep him beyond the reach of U.N. inspectors.
(This story is refiled to add name of think-tank in paragraph 10)
(Editing by Robin Pomeroy)