"Resistance sources have managed to uncover two centres that work directly on nuclear armaments and which were until now kept secret," Mehdi Abrihamtchi of the People's Mujahedeen told reporters in Paris, where his group is based.
"They are places for research and production of detonation systems which is a major part of the mullahs' atomic bomb project," he said, adding that his organisation had passed on the information to the UN atomic watchdog, the International Atomic Energy Agency.
The UN Security Council has ordered three rounds of sanctions for failing to end its uranium enrichment programme which the West sees as a cover for acquiring nuclear arms. Tehran says the programme is solely for electricity generation.
Abrihamtchi said the secret sites belonged to a unit linked to the defence ministry and called Research Centre for the Technology of Explosion and Impact, known as METFAZ.
The centre has a research unit, a production unit and a test unit, he said. Its command center was in a building in eastern Tehran.
The second site, surrounded by high concrete walls, is near the village of Sanjarian to the east of the capital, he said.
"In this site they build parts and units necessary for tests, using advanced technologies," he said.
The opposition figure provided an address in eastern Tehran as the site of a command and research centre where he said computer simulations were carried out.
He gave another location in the village of Sanjarian as the venue for the manufacture of components for detonation systems.
The manufactured explosives are tested at a special military facility in Parchin, southeast of Tehran which serves as "a cover for blast tests linked to non-conventional weapons," he added.
The opposition movement was the first to reveal the Islamic regime's nuclear programme in 2002.
