Mariupol, which has been encircled by Russian troops for weeks, has seen the fiercest fighting and most comprehensive destruction since Russia sent troops into Ukraine on Feb 24.

Ukrainian authorities said yesterday that no fewer than 1,000 civilians were hiding in underground shelters beneath the vast Azovstal plant, adding that Russia was dropping heavy bombs onto the Ukrainian-held factory in the besieged city.

Russia’s defence ministry today issued a statement calling on Ukrainian forces and foreign fighters inside to surrender.

“All who lay down their arms are guaranteed to remain alive,” the defence ministry said.

It called on troops to withdraw from the steel plant between 2pm and 4pm Moscow time “without exception, without any weapons and without ammunition”.

Earlier today, Russia-backed separatist forces said they were trying to storm the Azovstal steelworks and take control of it as quickly as possible.