The facility, called Behjatad-Abyek and code-named 311, is about 85 per cent complete and should be finished by the end of this year, said Alireza Jafarzadeh, who presented the information along with the the Iran Policy Committee.
Jafarzadeh said the information was provided by the People's Mujahedeen of Iran, which is backed by the Iran Policy Committee. The Mujahedeen opposes the Iranian regime and is listed by the US State Department as a terrorist organization.
Iran is installing centrifuges in the facility near Qazvin for enriching uranium, a process essential for building a nuclear weapon, Jafarzadeh said. He added that the Iranian government has not informed the International Atomic Energy Agency (IAEA) of the facility, a standard practice when building a nuclear site for producing civilian energy.
"This has no peaceful intentions whatsoever," Jafarzadeh said.
Jafarzadeh would not divulge the exact sources of the information, saying it would put lives in danger. He also said the information was provided to the US government and the IAEA but would not go into details.
He said the satellite images covering a period from 2004 to August show construction of tunnels and underground facilities designed to protect against an airstrike, and said defensive missiles were to be installed.
The United States and its allies suspect Iran is developing nuclear weapons, while Iran maintains its work is solely for producing energy. Iran has rejected UN Security Council demands to suspend uranium enrichment. The Security Council passed its latest round of sanctions against Iran in June.