LONDON (Reuters – Brightly lit white munitions were seen falling on the Azovstal Steel Works in Mariupol. It was a British military expert who said it looked like an incendiary or phosphorus attack.

Reuters couldn’t immediately identify which type of munitions were used and when the video was shot. Alexander Khodakovsky posted the video on Telegram, an application for messaging. He is a commander in the pro-Russian-sponsored republic of Donetsk.

Khodakovsky stated in a message that was posted alongside the video: “If you don’t know its purpose and what it is, then you can say that it’s beautiful.” Khodakovsky was not available for comment immediately.

The origin of the munitions and their source were not immediately known.

While Russian forces have pounded Mariupol over the past two months, some Ukrainian fighters are still trapped in Mariupol’s vast Soviet-era plant built under Josef Stalin. It is equipped with many tunnels and bunkers to resist attack and has a maze of bunkers.

Russia has yet to comment on which weapons were used against the plant. Russian defence ministry didn’t respond to an email request for comment on the video.

The Ukrainian Armed Forces declined to comment immediately.

On battlefields, white phosphorus can be used to create smoke screens, provide illumination, burn buildings and bunkers, or mark targets. International conventions do not prohibit white phosphorus from being used as a chemical weapons.

Because of their severe burns, human rights organizations have called for a ban of phosphorus weapons. Phosphorus munitions were used by the United States in both the Vietnam War and 2003-2011 wars in Iraq. These munitions were used in Russia’s Chechen wars.

An aide of Mariupol’s mayor Petro Andryushchenko claimed that Russia used incendiary and phosphorous bombs against Azovstal. Andryushchenko spoke from Ukrainian territory. Reuters couldn’t immediately verify Andryushchenko’s comments.

Hamish Stephen-Gordon, a former Commanding Officer of Britain’s Joint Chemical, Biological, Radiological and Nuclear Regiment, claimed that the footage looked very much like phosphorus, though only a specimen could confirm.

He said that it looked very similar to white phosphorus rockets and artillery shells, which were exploding above or below the ground.

He said, “It might be Russian incendiary missiles but I have seen white phosphorus in particular Syria and it seems very similar to that to me.”

Some Ukrainian fighters remain in bunkers at the Steel Plant, but civilians have been evacuated.