Moscow had agreed to exchange hundreds of members of the Azov Regiment – the Ukrainian unit holed up in the Soviet-era steel mill – in a prisoner swap earlier this week.

However Russia’s parliament has now announced it will vote on a resolution to ‘prevent the exchange of Nazi war criminals’ today – with some members calling for the Azov troops to be executed.

Ukraine’s deputy defence minister Hanna Malyar dismissed the threats as ‘internal propaganda’, adding that ‘an exchange procedure will take place’ as Kyiv abandons the steelworks after more than 80 days.

But experts have decried the move as ‘underhand’ and claimed it could scupper Ukraine’s bid to free the 600 soldiers – some of whom are still at the plant in Mariupol.