Russia has used a suspected chemical weapon in the besieged city of Mariupol, Ukraine claims.
Ukrainian troops defending the city are reportedly suffering respiratory failure, dizziness and other symptoms as a result of the 'unknown substance'.
It comes after multiple warnings that Russia may use chemical weapons to break the stalemate in Ukraine.
Pro-Russian separatist rebels said the Kremlin could use chemical weapons to defeat the Mariupol defenders.
Meanwhile, the MoD yesterday predicted that deadly phosphorus bombs could be used in attempt to break resistance.
On Monday evening, Ivanna Klympush, a Ukrainian MP, tweeted: "Russia 1.5hr ago used unknown substance in #Mariupol.
"Victims experience respiratory failure, vestib.-atactic syndrome. Most likely chem.weapons!
"This is red line beyond which must destroy economy of despotism.We demand full embargo on all fuels from #RU &heavy weapons 2UA now!"
Britain is now “working urgently” to verify reports that Russian forces may have launched a chemical attack in Ukraine, the UK Foreign Secretary has said.
Liz Truss became one of the first Western senior politicians to speak out last night as Britain warned “all options are on the table” if chemical weapons are confirmed.
It comes after unconfirmed reports from the besieged port city of Mariupol, whose mayor said more than 10,000 civilians have died in weeks of fighting.
On Monday evening, Ivanna Klympush, a Ukrainian MP, tweeted: " Russia 1.5hr ago used unknown substance in #Mariupol.
"Victims experience respiratory failure, vestib.-atactic syndrome. Most likely chem.weapons!
"This is red line beyond which must destroy economy of despotism. We demand full embargo on all fuels from #RU &heavy weapons 2UA now!"
The far-right Ukrainian Azov regiment said: "Russian occupation forces used a poisonous substance of unknown origin against Ukrainian military and civilians in the city of Mariupol, which was dropped from an enemy drone.
"The victims have respiratory failure... the effects of the unknown substance are being clarified."
In what appears to have been a chilling warning, Eduard Basurin, a spokesman for the pro-Russian Donetsk People’s Republic in eastern Ukraine, previously said the Kremlin may have to use chemical weapons to conquer Mariupol.
It comes after Ukrainian marines said they were surrounded by Russian soldiers in Mariupol.
The 36th marine brigade of the Ukrainian armed forces said it is now relying on cooks, drivers and other non-combat troops to fight the Kremlin's soldiers.
Kyiv estimates that tens of thousands of people have been killed in the Russian attack on Mariupol.
Much of the city has been devastated by Russian bombs, including the Mariupol theatre, where hundreds of people were killed.
The 36th marine brigade of the Ukrainian armed forces wrote on Facebook : "Today will probably be the last battle, as the ammunition is running out.
"It's death for some of us, and captivity for the rest."
The brigade earlier said it had been pushed back and surrounded by Russian forces, with around half of the contingent's men wounded, Mail Online reports.
It wrote on Facebook: "The infantry was all killed and the shooting battles are now conducted by artillerymen, anti-aircraft gunners, radio operators, drivers and cooks. Even the orchestra."
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The brigade added that troops whose 'limbs are not torn off' have returned to battled after being injured.
Commenting on the destruction in the city, President Volodymyr Zelensky said: "Mariupol has been destroyed, there are tens of thousands of dead, but even despite this, the Russians are not stopping their offensive."
At least 300 people taking shelter at a theatre in Mariupol were killed by a Russian airstrike as Vladimir Putin's war rages.
The Drama Theatre of Mariupol, where hundreds including children had been sheltering, was hit by the deadly airstrike last month.
Defence minister James Heappey praised the Ukrainian armed forces, describing their actions as "amazing heroism" and "extraordinary courage".
He told Sky News: "It's just the most monstrous loss of life that is a deliberate tactic used by the Russians to besiege cities and impose cost on the civilian population that has remained."
On arguments of genocide, he added: "I would just say that whatever is going on in Ukraine from the Russians is extraordinarily bleak and I think that the resolve of the Ukrainian people and President Zelensky to keep fighting and to win back their territory is amazing, the cost is enormous.
"Putin however, will be held to account and so too will everybody who serves in his government and the chain of command who have been responsible for these atrocities."
