Russia-Ukraine Crisis: Russia told Ukrainian forces holed up in a chemical plant in embattled Severodonetsk to lay down their arms by early Wednesday as it fights to maintain momentum in its battle for control of eastern Ukraine.

Ukraine is calling for an increase in Western heavy weapons after Russia committed the bulk of its firepower to the eastern Donbas region, a topic expected to feature prominently at a meeting of NATO defence ministers on Wednesday in Brussels.

Russian forces cut off the last routes for evacuating citizens from the eastern Ukrainian city of Severodonetsk, a Ukrainian official said, as the Kremlin pushed for victory in the Donbas region.

The last bridge to the city was destroyed, trapping any remaining civilians and making it impossible to deliver humanitarian supplies, said regional governor Sergei Gaidai, adding that some 70% of the city was under Russian control.