'Fortress in a city': Ukrainians cling on at steel plant in Mariupol

Explosions rumbled and smoke rose this week from a steel-making district in besieged Mariupol where dwindling Ukrainian forces are holed up as Russia tries to take full control of its biggest city yet.

The Azovstal iron and steelworks, one of Europe's biggest metallurgical plants, has become an aptly apocalyptic redoubt for Ukrainian forces who are outgunned, outnumbered and surrounded seven weeks into Russia's invasion of Ukraine.

In the east of the southern port devastated by weeks of shelling, the plant lies in an industrial area that looks out to the Sea of Azov and covers more than 11km2, containing myriad buildings, blast furnaces and rail tracks.

"The Azovstal factory is an enormous space with so many buildings that the Russians... simply can't...