The International Atomic Energy Agency (IAEA), the United Nations’ nuclear watchdog, said in a report that Iran may have built an extension to part of its Parchin nuclear site since May.

“Since (our) previous report (in May), at a particular location at the Parchin site, the agency has continued to observe, through satellite imagery, the presence of vehicles, equipment, and probable construction materials. In addition, a small extension to an existing building” appeared to have been built, the confidential IAEA report obtained by Reuters said.

The Parchin nuclear site was last visited by international inspectors in the year 2005. The latest revelation may jeopardize the IAEA’s ability to verify Western intelligence suggesting that Iran has carried out testing relevant to nuclear bomb detonations at the site. Iran has dismissed these claims as “fabricated.”

The new IAEA report is just the latest controversy over the Parchin nuclear site. Last week the Associated Press revealed an undisclosed agreement between the IAEA and Iran that would allow the Islamic Republic to conduct nuclear inspections at the Parchin nuclear site. Israel has demanded that the IAEA publish those undisclosed agreements.

The government of Israel considers a nuclear Iran to be an existential threat.