More than 1,000 Ukrainian marines have surrendered in the port of Mariupol, Russia's defence ministry said on Wednesday of its main strategic target in the eastern Donbas region, which has been reduced to ruins but is not yet under Russian control.

If the Russians take the Azovstal industrial district, where the marines have been holed up, they would be in full control of Mariupol, Ukraine's main Sea of Azov port, allowing Russia to reinforce a land corridor between separatist-held eastern areas and the Crimea region that it seized and annexed in 2014.