The Iranian Defense Ministry offered no information on who it suspected carried out the attack, which came as a refinery fire separately broke out in the country’s northwest, and a 5.9 magnitude earthquake struck nearby, killing three people.

However, Tehran has been targeted in suspected Israeli drone strikes amid a shadow war with its Middle Eastern rival as its nuclear deal with world powers collapsed.

Meanwhile, tensions remain high with neighboring Azerbaijan after a gunman attacked that country’s embassy in Tehran, killing its security chief and wounding two others.

Details on the Isfahan attack, which happened around 11:30 p.m. local time Saturday, remained scarce. A Defense Ministry statement described three drones being launched at the facility, with two of them successfully shot down.

A third apparently made it through to strike the building, causing “minor damage” to its roof and wounding no one, the Ministry said.

Iranian state television’s English-language arm, Press TV, aired a mobile phone video apparently showing the moment that drone struck along the busy Imam Khomeini Expressway that heads northwest out of Isfahan, one of several ways for drivers to go to the holy city of Qom and Tehran, Iran’s capital.

A small crowd stood gathered, drawn by anti-aircraft fire, watching as an explosion and sparks struck a dark building. “Oh my God! That was a drone, wasn’t it?” the man filming shouts. “Yeah, it was a drone.”

Those there fled after the strike. That footage of the strike, as well as footage of the aftermath, corresponded to a site on Minoo Street in northwestern Isfahan that’s near a shopping center that includes a carpet and an electronics store.

Iranian defense and nuclear sites increasingly find themselves surrounded by commercial properties and residential neighborhoods as the country’s cities sprawl ever outward.

Some locations also remain incredibly opaque about what they produce, with only a sign bearing a Defense Ministry or paramilitary Revolutionary Guard logo.

The Defense Ministry only called the site a “workshop,” without elaborating on what it made.

Isfahan, some 350 kilometers south of Tehran, is home to both a large air base built for its fleet of American-made F-14 fighter jets and its Nuclear Fuel Research and Production Centre.

The attack comes after Iran’s Intelligence Ministry in July claimed to have broken up a plot to target sensitive sites around Isfahan.

A segment aired on Iranian state TV in October included purported confessions by alleged members of Komala — a Kurdish opposition party that is exiled from Iran and now lives in Iraq — who said they planned to target a military aerospace facility in Isfahan after being trained by Israel’s Mossad intelligence service.

Activists say Iranian state TV has aired hundreds of coerced confessions over the last decade. Israeli officials declined to comment on the attack.

Separately, Iran’s state TV said a fire broke out at an oil refinery in an industrial zone near the northwestern city of Tabriz.

It said the cause was not yet known, as it showed footage of firefighters trying to extinguish the blaze. Tabriz is some 520 kilometers northwest of Tehran.

State TV also said the magnitude 5.9 earthquake killed three people and injured 816 others in rural areas in West Azerbaijan province, damaging buildings in many villages.