Recent satellite photos show continued activity at a controversial Iranian military site that international weapons inspectors have repeatedly been denied access to, according to a Washington-based think tank.

The Institute for Science and International Study obtained imagery from DigitalGlobe taken on November 7 that the institute says shows changes in the roofs on two key buildings at the Parchin Military Complex. ISIS also pointed out there is a new addition on the building suspected of containing a high-explosives chamber and piles of dirt not seen in an image taken on September 19.

ISIS said the imagery indicates additional changes will be made to the site, making it more difficult for the international inspectors.

"The considerable amount of new materials, equipment, and rows of earth piles suggest that further construction will be taking place, thus increasing the level of alteration and further degrading the chance of obtaining reliable environmental samples if and when (International Atomic Energy Agency) inspectors gain access to the site," ISIS stated.

Since January, the IAEA has been seeking access to the site, where it suspects Iran may have conducted high-explosives tests related to the development of nuclear weapons. Iran denies that Parchin has any role in its nuclear program.

The latest IAEA report on Iran released earlier this month said the "extensive activities" at the Parchin site are certain to have "seriously undermined" the agency's verification process.

Those activities include "significant ground scraping and landscaping" with new dirt roads.