Elements of Ukraine's Armed Forces and several hundred civilians are sheltering in underground bunkers in Azot Chemical Plant in the embattled city of Sievierodonetsk, Britain's defence ministry said on Wednesday.

Russian forces now control the majority of the Ukrainian city, Britain's Ministry of Defence said in a Twitter update.

Russia told Ukrainian forces who were holed up in the chemical plant to lay down their arms by early Wednesday, pressing its advantage in the battle for control of eastern Ukraine.

(Reporting by Baranjot Kaur in Bengaluru; Editing by Tom Hogue)