Iranian Foreign Minister Mohammad Javad Zarif said Saturday that opponents of the Iran nuclear deal have been spreading "lies" about activity at its secretive Parchin military site.

"We said that the activities in Parchin are related to road construction," Zarif was quoted as saying by the IRNA state news agency, reported Reuters.

Parchin is a highly secretive Iranian military installation that has long been suspected of being involved with nuclear weapons research, as HNGN previously reported.

The latest accusations over activity at the site came Friday when the U.S.-based Institute for Science and International Security think tank said that satellite images suggest Iran could be involved in a nuclear cleanup effort at Parchin before officials from the U.N.'s International Atomic Energy Agency (IAEA) arrive to inspect the site. The group cited images of crates, heavy machinery, trucks and construction as being indicative of a cleanup effort rather than road construction.

The U.S. intelligence community also informed Congress last week of the satellite images, taken in mid and late July, and concluded with high confidence that Iran was sanitizing the site ahead of an IAEA visit, according to Bloomberg.

"They (opponents of the deal) have spread these lies before. Their goal is to damage the agreement," Zarif added.

The Institute for Science and International Security quickly took to Twitter to deny that it was an opponent of the deal, tweeting, "We are neutral."

As part of the recently concluded nuclear accord reached between Iran and six world powers, IAEA and Iran entered a secret side deal meant to resolve past suspicions about the site. U.S. lawmakers have expressed concern over the side deal because the text has not been made available to Congress or any of the countries P5+1 countries involved in the negotiations.