TEHRAN — A mysterious explosion at or near an important military complex rocked the Iranian capital on Sunday, lighting up the skies over the city.

Iranian official sources denied the explosion had taken place at the complex, the expansive Parchin military site east of the city, where international monitors suspect Iran once tested triggers for potential nuclear weapons. But the enormous orange flash that illuminated Tehran around 11:15 p.m. local time clearly came from that direction, several witnesses said.

Officials at Iran’s Defense Industries Organization, though also denying that the explosion took place at Parchin, confirmed that two people were missing after “an ordinary fire” caused by “chemical reactions of flammable material” at an unspecified production unit, according to the semiofficial Iranian Students’ News Agency. There was no word on the location of the fire.

Witnesses in the east of Tehran said that windows had been shattered in the vicinity of the military complex and that all trees in a hundred-yard radius of two villages, Changi and Hammamak, had been burned. The villages are on the outskirts of the military site.