The fire broke out near the city of Mashhad, in a storage facility. According to some reports, the smoke covered "the whole city" It is unclear exactly where the fire was and whether it is a site linked to the nuclear program.
In the past Iran has accused Israel of mysterious explosions at sites connected in one way or another to its nuclear program or missile system. It was also reported that there were no casualties, but no further details were given. The city's name has come up in the nuclear context, but in the past the tweets actually attributed the event to the mass protests.