Vladimir Putin could be “setting the scene” for the use of chemical or biological weapons in Ukraine, according to Western officials.
Officials said on Wednesday they were “very concerned about the risk of escalation” as the humanitarian situation worsened and the Russians “tighten the noose” around Kyiv.
“We have good reasons to be concerned about possible use of non-conventional weapons,” one official said. “It’s a serious concern for us.
“We see a bit of setting the scene for that in the false flag claims that are coming out.”
The official said Western worries were based on what had happened during the war in Syria, which saw the use of chemical weapons.
It came as Ukrainian president Volodymyr Zelenskyy accused Russia of hitting a maternity hospital in Mariupol in the south east of his country.
“Direct strike of Russian troops at the maternity hospital. People, children are under the wreckage,” he said. “Atrocity!
“How much longer will the world be an accomplice ignoring terror? Close the sky right now! Stop the killings! You have power but you seem to be losing humanity.”
Nato has so far ruled out imposing a no-fly zone over Ukraine as Zelenskyy has requested, amid warnings it would lead to a direct war between the West and Russia.
Earlier, defence secretary Ben Wallace announced the UK was sending more weapons to Ukraine to help its effort against the Russia’s invasion.
He told MPs that the UK has delivered 3,615 anti-tank weapons and will shortly be supplying a “small consignment” of Javelin anti-tank missiles.
“In response to a Ukrainian request, the Government has taken the decision to explore the donation of Starstreak high-velocity manned portable anti-air missiles,” Wallace added.
“We believe that this system will remain within the definition of defensive weapons but will allow the Ukrainian force to better defend their skies.”
Travelling at more than three times the speed of sound, according to the British Army, Starstreak can be shoulder-mounted or attached to a vehicle.
It was deployed during the London Olympics in 2012, positioned on rooftops near the Olympic stadium.