A senior Ukrainian police officer has accused Russia of using banned white phosphorus bombs in attacks on Ukraine's eastern region of Lugansk.
The use of the banned shells is prohibited for use in heavily populated civilian areas under international law but is allowed in open spaces for use as cover for troops.
Oleksi Biloshytsky, head of police in Popasna, 95 kilometres west of Lugansk city, said that Russian forces had used the chemical weapon in his area.
In a post on Facebook, he said: "It's what the Nazis called a 'flaming onion', and that's what the Russcists (an amalgamation of 'Russians' and 'fascists') are dropping on our towns. Indescribable suffering and fires."
The claims are yet to be verified.
The news comes after Polish President Andrzej Duda said the use of chemical weapons by Moscow in its invasion of Ukraine would be "game-changing" and must encourage NATA to rethink the conflict.
He told BBC if Russian President Vladimir Putin "uses any weapons of mass destruction, (it) will be game-changing in the whole thing... for close alliances".
He added: "Because then it starts to be dangerous, not only for Europe, not only for our part of Europe... but for the whole world."
Mr Duda warned that Putin could use extreme means to win the war as he has already lost the conflict "politically".
He also said around five million refugees could flee Ukraine as the war continues, with half of them expected to remain in Poland.
Poland has so far taken in 1.7 million refugees since the beginning of the invasion.
Mr Duda said: "More than half of all refugees who have left Ukraine are in Poland. So if there are five million, then just imagine that we will get 2.5 million."
He added: "It is hard for me to imagine. So we need support here on the ground. We need kind help, financial assistance."
Speaking on the BBC's Sunday Morning show, President Duda said: "This is something that the world has not seen on this scale since the Second World War.
"If you're asking can Putin use chemical weapons, I think that Putin can use anything right now, especially because he's in a very difficult situation."
He added: "Although one can say that there is a gigantic advantage of the Russian army over the Ukrainian army.
"If you take a piece of paper and you do the math, then they have a crushing, overwhelming majority, but they are not able to win the war."