The facility at Khojir, a defense-ministry missile-research site on the southeast edge of Tehran, is developing a nuclear warhead for use on Iranian medium-range missiles, according to Mohammad Mohaddessin, foreign-affairs chief for the exiled National Council of Resistance of Iran

He also said the NCRI has identified a guest house on a military compound near Khojir that the group says houses North Korean specialists working at the warhead facility

The NCRI is the Paris-based political wing of the Mujahedin e-Khalq, an exiled military group that has been seeking to overthrow the current Iranian regime since the mid-1980s. The U.S. and the European Union list the group as a terrorist organization

The commercial satellite images depict a system of heavy security within the Khojir site restricting access to the alleged nuclear-warhead facility. Visitors to the facility -- which is known as "Eight-five hundred" -- have to leave their cars and drivers behind at the car park