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

By Natalia Zinets

April 15 (Reuters) - 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 steel works, 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 11 square kilometres (4.25 square miles), 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 find (the Ukrainian forces)," said Oleh Zhdanov, a military analyst based in Kyiv.

"That's why they (the Russians) started talking about trying a chemical attack, that's the only way to smoke them out," Zhdanov said.

Ukraine has said it is checking unverified information that Russia may have used chemical weapons in Mariupol. Russia-backed separatists have denied using chemical weapons.

In peace time, the Azovstal iron and steel works pumped out 4 million tonnes of steel a year, 3.5 million tonnes of hot metal and 1.2 million tonnes of rolled steel.

Like the city's other Illich Steel and Iron Works, Azovstal is held by Metinvest, the group controlled by billionaire Rinat Akhmetov, Ukraine's richest man.

A Russian separatist deputy commander said on Russian state TV on Monday that Moscow had captured 80% of the port, but that resistance continued and that Ukrainian forces had all tried to "exit towards the Azovstal factory".

He described the factory as a "fortress in a city".

The city's defenders include Ukrainian marines, motorised brigades, a National Guard brigade and the Azov Regiment, a militia created by far-right nationalists that was later incorporated into the National Guard.

It is the Azov Regiment, whose destruction is among Moscow's war objectives, that is prominently associated with Azovstal and one of its founders, Andriy Biletskiy, has also called it "the fortress of the Azov".

Russian President Vladimir Putin calls the invasion a "special operation" for the "demilitarisation and denazification of Ukraine" but Ukraine and the West say Russia launched an unprovoked war of aggression.