Russia is allegedly using phosphorous weapons to strike the besieged city of Bakhmut, according to Ukraine.
The city of Bakhmut is seen on fire as what seems to be white phosphorous pours down on it in drone footage provided by the Ukrainian military.
Although the use of white phosphorus weapons in residential areas is not prohibited, it is seen as a war crime.
They start flames that spread quickly and are particularly challenging to put out. Previously, Russia has been charged with employing them.
Despite Bakhmut's dubious strategic relevance, Russia has been attempting to seize it for months. Thousands of Moscow's soldiers are thought to have perished in the assault, according to Western authorities.
The Ukrainian defense ministry said the strike had used incendiary ammunition to target "unoccupied areas of Bakhmut," writing on Twitter.
When it occurred is unknown. However, the video that Ukraine published, which appeared to have been taken by a surveillance drone, showed tall structures that were on fire.
In other footage shared on social media, flames could be seen blazing on the ground and white clouds could be seen lighting up the night sky.
An examination of the film revealed that it was shot in a location just west of the core of Bakhmut and adjacent to a children's hospital. The study was able to determine that some sort of incendiary munitions were employed in the attack, but it was unable to confirm the use of phosphorus.
White phosphorous has been linked to Russian usage in Ukraine, especially during the siege of Mariupol at the start of the conflict.
Moscow has never openly acknowledged deploying the drug, and when Ukrainian President Volodymyr Zelensky claimed it had been used, Kremlin Press Secretary Dmitry Peskov asserted "Russia has never violated international conventions."
A wax-like material called white phosphorus burns at 800C and ignites when it comes in touch with oxygen, producing brilliant plumes of smoke.
The chemical is "notorious for the severity of the injuries it causes," according to Human Rights Watch (HRW).
When bandages are taken off, it can re-ignite and is very sticky and difficult to remove.
Russia has ratified the Convention on Certain Conventional Weapons, which forbids the use of incendiary weapons in civilian areas. Incendiary weapons are those that are intended to set things on fire.
White phosphorus, however, according to HRW, is exempt from the treaty since its main use is to "create a smokescreen to conceal military operations."
According to HRW, US forces have used the chemical "repeatedly over the past 15 years" on IS fighters in Iraq and Syria.
Its employment as an incendiary weapon close to civilians, according to some observers, would still be prohibited. There are hardly any citizens remaining in Bakhmut, which had 80,000 residents before the conflict.
In a dispute over ammunition supply, the leader of Russia's Wagner paramilitary squad said the next day that he would withdraw his soldiers from Bakhmut on May 10.
Wagner's fatalities, according to Yevgeny Prigozhin, were "growing in geometrical progression every day" and he had decided to leave because of pressure from the military minister.
Prigozhin said on Saturday that Ramzan Kadyrov, the head of Russia's semi-autonomous Chechnya province, had consented to seize Wagner's positions in the city and swap out his soldiers with Wagner's.
He was cited by Prigozhin's press agency as stating, "I am already contacting his representatives to start transferring positions immediately, so that at 00:00 on May 10."
Despite his assertions, Ukrainian authorities said Wagner had sent mercenaries back in the direction of Bakhmut in an effort to seize the city ahead of Tuesday's Victory Day festivities in Russia.
Deputy Defence Minister Hanna Maliar reported that "we are now seeing them pulling [fighters] from the entire offensive line where the Wagner fighters were, and they are pulling [them] to the Bakhmut direction."
There are rumors that Ukraine is preparing a massive counteroffensive as the battle continues. According to Prigozhin, the strike might occur as early as May 15.
The Zaporizhzhia area, which is mostly under Russian control, may see an attack.
The evacuation of settlements close to the battle line was ordered by the Russian-installed governor of Zaporizhzhia on Friday.
After phony referendums and an illegal annexation last year, Russia now views the region as its own.