Iran’s claim that it is performing road work at its Parchin military site came under question Friday by a prominent US think tank, which noted independent satellite imagery did not support the explanation, Israel Hayom reported. Instead, the Institute for Science and International Security said it appears the Islamic Republic is trying to sanitize the site ahead of announced international inspections.

The Parchin site has faced the suspicions of many countries as being used for nuclear experimentation, a claim Iran flatly denies. Recent vehicle movement at the site was explained away as road work near the Mamloo Dam.

The Institute for Science and International Security, however, issued a fresh analysis of the situation, saying in a statement, “Commercial satellite imagery does not support the Iranian explanation. [The Institute] analyzed commercially available satellite imagery taken on July 12, 19, and 26, 2015 but did not find any visible signatures related to road work on the road near the dam.”

The group also found it suspicious for Iran to “park vehicles three kilometers south of the dam and at the one site that would create intense concern and suspicion about Iran’s intentions to comply with the recently negotiated [deal].

“There is no support in the imagery for the Iranian explanation,” the Institute’s new analysis said. “Iran’s explanation appears to be that the vehicles at the suspect site were there inadvertently, but this explanation strains believability.”

The Islamic Republic rejected the Institute’s conclusions.  Representatives of the Iranian UN mission had nothing to add in response, while Iranian Foreign Minister Mohammad Javad Zarif Saturday called the Institute’s statement “lies” spread by opponents of the nuclear deal.

“We said that the activities in Parchin are related to road construction,” Zarif was quoted as saying by the state-run Islamic Republic News Agency. “They [opponents of the deal] have spread these lies before. Their goal is to damage the agreement.”

The Institute was quick to point out on Twitter that it was not one of the deal’s opponents. “We are neutral,” the think tank posted.

The International Atomic Energy Agency (IAEA) requested access to the Parchin military site as part of the nuclear deal signed on July 14. The Institute believes Iran is trying to clean up the site ahead of any IAEA inspection.

Iran’s parliamentary speaker rejected the Institute’s explanation. “This is an artificial dispute to distract the world,” Ali Larijani was quoted on Saturday by the Fars News agency as saying. He accused Israel, which has publicly decried the accord reached between Iran and the P5+1 powers, of trying to stop it from being implemented.