The Washington-based Institute for Science and International Security has posted satellite images on its website that suggest Iran is attempting to destroy evidence of possible nuclear weapons research at a site UN inspectors have not been allowed to visit.
The images appear to show that Iran has demolished two buildings at the Parchin military installation southeast of Tehran.
The Parchin facility has received greater international attention since last year when images first showed a clean-up in progress there shortly after inspectors from the International Atomic Energy Agency (IAEA) first requested permission to visit the site.
Iran refused both that request and subsequent requests to visit the site, insisting Parchin was an ordinary military facility.
The latest satellite images of Parchin were shown to the IAEA's 35-member board at a closed-door session on May 30.
Based on reporting by Reuters and AP