Yesterday, unconfirmed reports emerged that Russia had used chemical weapons in the besieged Ukrainian port of Mariupol.

The alarm was raised by Ukrainian soldiers who claimed a Russian drone flew overhead releasing a cloud of smoke and that three soldiers were left with breathing difficulties.

Under the Geneva Protocol, the use of chemical and biological weapons is prohibited in international armed conflicts.

Ukraine president Volodymyr Zelensky has called for the west to impose even tougher sanctions that will deter the Kremlin from even talking about escalating the conflict to the use of chemical weapons.

Today on Please Explain, foreign affairs correspondent Anthony Galloway, who has recently reported from Ukraine, joins Nathanael Cooper.