Pro-Russian separatists from Donetsk published the film on the Telegram app on Sunday.
"If you did not know what it was and for what purpose, you could say that it is even beautiful," writes a commander of the separatists.
Rein Pella, a teacher at the Swedish National Defense College, says that it is a rather small and insignificant attack.
Not many rockets are fired, and in addition, large parts of the ammunition miss the target, he says.
- By filming it with drones, it is a pretty spectacular attack.
I can imagine that a large part of the purpose is simply propaganda filming for the Russians.
The weapons expert: These are not phosphorus bombs
The news agency Reuters has verified the place that the film shows, but could not confirm when it was recorded.
Authorities in Mariupol have said that it is phosphorus bombs that Russia has dropped on the steel plant, but Rein Pella, for his part, believes that it is unlikely.
- No, it's not phosphorus.
When phosphorus burns, a very white thick smoke is created, he says.
- What we see in the film are termite rockets, that is, firebombs.
It is previously known that the Russians have and use termite rockets, he says.
International law prohibits the use of phosphorus bombs in densely populated areas, but in open places as protection for military troops they are allowed.
Russia has not commented on the specific weapons used to attack the facility.
The situation remains critical in the steelworks
The steelworks is the only part of Mariupol that is not under Russian control.
Denys Shlega, a Ukrainian commander, says that Russian troops have penetrated parts of the steelworks, but that it has not been given a significant role yet.
He describes the conditions in the steelworks as difficult.
– För tillfället har vi cirka 600 personer som är skadade. Ett 40-tal är i ett mycket allvarligt tillstånd, säger han till ukrainsk tv.