Iranian officials are investigating an explosion that turned the skyline east of the capital, Tehran, a bright orange for several seconds this morning, official news agencies reported.
A spokesman for the Defense Ministry, Brig. Gen. Davoud Abdi, told state television that a gas explosion had occurred in the general area of Parchin, a military and weapons development base, but that there were no casualties and the fire was under control.
"Our colleagues are present on the ground and investigating the incident carefully," Abdi said.
Many residents of Tehran and surrounding suburbs posted accounts on social media asking if others had seen the sky suddenly turning orange or had heard two booms.
"We suddenly saw this scene and we were all terrified," tweeted Hamid Reza, who posted a video of the aftermath that he shot from a mountaintop in northern Tehran.
Tehran's head of emergency response told local news outlets that workers had received no immediate requests for ambulances or medical aid but were on standby.
Parchin has been the focus of contention in the past. For years, Iran refused to grant access to inspectors from the International Atomic Energy Agency, saying that as a military base it was off limits.
In 2014, a huge explosion caused damage there and raised questions of sabotage, but international investigators were denied access.
rockets, atomic tests
"Parchin is basically the largest military explosive manufacturing site in Iran," said Fabian Hinz, a researcher at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies in Monterey, Calif. "They produce artillery rockets there, and had tests related to nuclear weapons designs before 2003."
By the time the head of the atomic energy agency was allowed to visit the site in 2015, it was empty.
An archive of the country's nuclear activity -- which Israel said its intelligence agents stole three years later -- included photos that appeared to show a giant metal chamber built to conduct high-explosive experiments in a building at Parchin.