Western intelligence officials and United Nations inspectors said they suspect Iran is planning to build more nuclear sites, according to The New York Times.
This comes despite international demands for the Islamic Republic to open up its nuclear operations for inspection.
Comments by the head of Iran's Atomic Energy Organization, Ali Akbar Salehi, prompted inspectors to search for at least two more sites.
Salehi told the Iranian Student News Agency in an interview that Iranian President Mahmoud Ahmadinejad had ordered two new plants built inside mountains.
"God willing," Salehi said, "we may start the construction of two new enrichment sites" in the Iranian new year, which began March 21.
Meanwhile, Tehran continues to insist its nuclear program is for peaceful purposes.