(JTA) — An explosion at or near an Iranian military complex believed to be a site for nuclear testing created a large orange flash over Tehran.

The New York Times reported that the explosion on Sunday night came from the direction of the Parchin complex, where Iran has been accused of testing nuclear weapons.

Iranian officials denied the explosion originated there.

Iran’s Defense Industries Organization said that two people were missing after “an ordinary fire” caused by “chemical reactions of flammable material” at an unspecified location, the Times reported.

Witnesses near the site said that windows had been shattered in the vicinity and that all trees in a hundred-yard radius of two villages on the outskirt of the military facility were burned.

The United Nations’ International Atomic Energy Agency inspectors visited Parchin in 2005, but since then have not been allowed to return, despite repeated requests.