Russia could soon use phosphorus munitions in Mariupol, the southern port city it's been trying to control for weeks, UK warns

• Russia may soon use phosphorus munitions in Mariupol, UK intelligence warned.
• The substance is strong enough to burn human flesh.

The UK warned that Russia may soon use phosphorus munitions in Mariupol, the strategically important Ukrainian city that Russia has been trying for weeks to seize.

The UK Ministry of Defence warned on Monday that Russia's previous use of the dangerous substance elsewhere in the Donetsk oblast — the eastern region where the port city of Mariupol is located — suggests that Russia may do the same in Mariupol.

The ministry said in a Monday intelligence update: "Russian forces prior use of phosphorous munitions in the Donetsk Oblast raises the possibility of their future employment in Mariupol as fighting for the city intensifies."

It also warned that Russia's "reliance on unguided bombs" in Ukraine increases the risk of killing more civilians.

Mariupol has been the scene of some of the most intense fighting in Ukraine since Russia invaded in late February. The city's maternity hospital was attacked, in what Ukrainian President Volodymyr Zelenskyy called a war crime, and citizens have been trapped in the city.

Mariupol's mayor said that at least 5,000 residents — including 210 children — had been killed since the invasion. Ukraine also said that Russia used mobile crematoriums there to hide civilians' bodies.

The danger of using phosphorus is how easily it causes fires, and how hard to those fires are to extinguish.

Stephen Goose, the director of the arms division of Human Rights Watch, told the United Nations in 2018: "It can burn people to the bone and reignite in cleaned wounds once bandages are removed."

Erik Tollefsen, the head of the weapons contamination unit for the International Committee of the Red Cross, told Newsweek in 2019: "It's extremely painful."

"I've seen these burns first-hand when trying to assist and provide first aid to the victims of these attacks and it's devastating ... It burns deep, deep, deep into the body and the trauma it causes can be severe."

The US also uses the substance, and it has legal uses in war, including to create light to brighten areas at night.

Zelenskyy told NATO last month that Russia had used "phosphorus bombs."

Pavlo Kyrylenko, the governor of Donetsk oblast, said in late March that Russia was using phosphorus ammunition in the area.