Satellite images obtained by a U.S. research organization suggest Iran may be trying to wipe traces of nuclear weapon testing from a key military site.

The Washington-based Institute for Science and International Security (ISIS) said the images, published on its website Thursday, show evidence “two small buildings at the same site as the suspected testing chamber have been razed.”

The ISIS report also said “heavy machinery tracks and extensive evidence of earth displacement” can be seen throughout the site, part of Iran's Parchin military complex.

ISIS says the satellite images were taken May 25 and support other images from April that indicated Iran had begun clean-up activities at the Parchin site. It also says the new images “raise further concerns of Iranian efforts to destroy evidence of alleged past nuclear weaponization activities.”

Western powers suspect Iran has engaged in atomic weapons research at the Parchin complex and the International Atomic Energy Agency has been trying to negotiate access to the site. Tehran says Parchin is a conventional weapons facility and insists the Iranian nuclear program is peaceful.

World powers agreed with Iran to hold more talks on the issue in June. Iran's delegation to last week's Baghdad negotiation claimed it offered its own proposal for ending the dispute.

Iranian state media said the delegation received no response to its offer.

Western powers fear Iran could quickly upgrade its uranium to the 90 percent purity needed for nuclear weapons. Iran wants an easing of international sanctions in return for any concession on enrichment work, which it says is meant for medical research and generating electricity.