Ukraine accused Russia of attacking the besieged city of Bakhmut with phosphorous munitions.

In drone footage released by the Ukrainian military, Bakhmut can be seen in flames with what appears to be white phosphorus raining down on the city.

White phosphorous weapons are not prohibited, but their use in civilian areas is a war crime.

They create fast-spreading fires that are difficult to put out. Russia has been accused of using it before.

Russia has been trying to take control of Bakhmut for months, despite its questionable strategic value. Western officials estimated that thousands of Moscow soldiers were killed in the offensive.

The Ukrainian Defense Ministry said on Twitter that the phosphorous attack targeted "uninhabited areas of Bakhmut with incendiary ammunition".

Military forces special forces in Kiev military forces continue to "destroy the city".

It was not clear exactly when the alleged attack took place. But footage shared by Ukraine - apparently taken by a reconnaissance drone - showed tall buildings on fire.

Other videos posted on social media showed fires raging on the ground.

Russia has been accused of using white phosphorous several times since the start of the war.

The head of the Wagner Group says that he will withdraw the fighters from Bakhmut

The attack comes a day after the commander of the Russian paramilitary group Wagner announced that he would withdraw his forces from Bakhmut on May 10, respectively, regarding ammunition supplies.

Yevgeny Prigozhin said that Wagner's losses were "increasing geometrically every day," and he commented his decision to withdraw from Bakhmut directly on the Ministry of Defense.

Despite Prigozhin's claims, senior Ukrainian officials said Wagner was redeploying mercenaries in the direction of Bakhmut in an attempt to capture the city ahead of Russia's Victory Day celebrations on Tuesday.

Defense Ministry Hanna Malyar told Ukrainian television.

The heavy fighting comes amid reports that Ukraine is preparing to launch a large-scale counteroffensive in the coming weeks. Prigozhin himself said he thought the attack might come as soon as May 15.

An offensive would occur in the Zaporizhzhya region, which is controlled by 80%.

On Friday, the Russian-installed governor of Zaporizhia region said he had ordered the evacuation of villages near the front line.

Russia considers the region its own territory, after self-described referendums and illegal annexation last year.