"In order to hide its nuclear activities, the Iranian regime is currently in the process of a vast operation moving the centre responsible for research and planning of the military nuclear project," Mehdi Abrishamachi of the National Council of Resistance of Iran told a press conference in Paris.
According to the opposition group, which has made significant revelations about Iran's nuclear programme in the past, the bulk of the centre's activities have been moved from a defence ministry property in the east of Tehran to a new site around three kilometres (two miles) away.
Those activities left at the first site could all be regarded as of dual-use -- related to either civil or military uses of nuclear technology -- enabling the regime to disguise their military nature in the event of inspection, according to the NCRI.
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"The transfer started at the beginning of September and is not finished but the essential has been done," Abrishamachi said.
The NCRI said it had submitted its information, including a list of 100 alleged employees of the centre, to the International Atomic Energy Agency on Wednesday.
Iran denies seeking to develop a nuclear weapons capacity and has said it wants to sign a nuclear proliferation accord with the West. Negotiations on the subject between Tehran, the five permanent members of the UN Security Council and Germany, are due to resume next week in Geneva.
The talks will be the first since the election in June of new Iranian President Hassan Rouhani.