BBC – Geographically, the city of Mariupol occupies only a tiny area on the map but it now stands obstinately in the way of Russian forces who have burst out of the Crimean peninsula.
They are pushing north-east to try to link up with their comrades and Ukrainian-separatist allies in the Donbas region of eastern Ukraine.
General Sir Richard Barrons – former commander of UK Joint Forces Command – says capturing Mariupol is vital to Russia’s war effort.
