An exiled Iranian opposition group Tuesday accused Tehran of running a "secret" uranium enrichment site close to Tehran, which it said violated ongoing talks with global powers on a nuclear deal. "Despite the Iranian regime's claims that all of its enrichment activities are transparent ... it has in fact been engaged in research and development with advanced centrifuges at a secret nuclear site called Lavizan-3," said Alireza Jafarzadeh, deputy director of the National Council of Resistance of Iran (NCRI).