An exiled Iranian opposition group said on Wednesday that a facility in Tehran that the United States suspects is involved in nuclear weapons research has been moved to avoid detection by the United Nations atomic watchdog.The dissident National Council of Resistance of Iran (NCRI) exposed Iran's uranium enrichment plant 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. Iran says allegations of nuclear bomb research are baseless and forged by its enemies.Iran and six world powers are to meet in Vienna next week as part of efforts to end a protracted and volatile impasse over Tehran's nuclear program, ahead of a Nov. 24 deadline for a comprehensive diplomatic settlement.The Islamic Republic says its nuclear energy program is a peaceful project to generate electricity.Citing information from sources inside Iran, the Paris-based NCRI said a nuclear weaponisation research and planning center called the Organisation of Defensive Innovation and Research (SPND) was shifted in July to a secure site in a defense ministry complex about 1.5 km (1 mile) from its former location. The NCRI had reported in October 2013 that Iran had begun moving the center.It said the SPND, which was mentioned in a UN nuclear agency report in 2011, had also reduced the profile of its chief Mohsen Fakhrizadeh, whose office was now at separate location. To help divert attention from key elements of the center, it said, Iran had left "non-sensitive" sections at the old site.The United States added the SPND to its sanctions list in late August. The move came after Iran failed to meet an Aug. 25 deadline to answer questions from the UN International Atomic Energy Agency (IAEA) about suspected nuclear bomb research."The fact this operation is working at full speed and that Fakhrizadeh is running the apparatus shows Iran does not want to be transparent in its nuclear program to the IAEA," NCRI spokesman Shahin Gobadi said."PRIMARILY RESPONSIBLE"The US State Department said on Aug. 29 the SPND "is primarily responsible for research in the field of nuclear weapons development" in Iran. It said it was run by Fakhrizadeh, who is on UN and US sanctions lists, after "managing activities useful in the development of a nuclear explosive device".Western officials and experts believe that Fakhrizadeh, a shadowy figure believed to be a senior officer in the elite Revolutionary Guards, has played a pivotal role in suspected Iranian work in the past to develop the means to assemble a nuclear bomb behind the facade of a declared civilian uranium enrichment program.Gobadi said his group over the last month had handed a document to the IAEA detailing what the NCRI called Tehran's concealment efforts. There was no immediate comment from the Vienna-based UN watchdog, which for years has been investigating alleged nuclear arms research by Tehran.A high-level IAEA team is in Tehran for talks this week to make a new attempt soon to advance its long-running investigation. The Iranian embassy in Paris was not immediately available for comment on the NCRI report.