Taking the Azovstal industrial district, where the marines have been holed up, would give the Russians full control of Mariupol, Ukraine's main Sea of Azov port, and reinforce a southern land corridor before an expected new offensive in the country's east.
Surrounded and bombarded by Russian troops for weeks and the focus of some of the fiercest fighting in the war, Mariupol would be the first major city to fall since Russia invaded Ukraine on 24 February.
