Conquering Mariupol will 'take time': separatist official

A pro-Russian separatist official in eastern Ukraine said Thursday it was impossible to say how long it could take Moscow's forces to fully seize the besieged city of Mariupol.

Mariupol, located in the country's southeast between Russia-occupied Crimea and pro-Russian separatist regions in Ukraine's east, has been the scene of some of the fiercest fighting.

Most recently, fighting has centred around the city's Azovstal iron and steel works and port, said Eduard Basurin, a senior official in the self-proclaimed breakaway stronghold of Donetsk.

In televised remarks, he described Mariupol's industrial zone as a "city within a city."

"Several floors were built underground during the Soviet Union. It is impossible to bomb from above, you need to do a cleanup operation underground," Basurin told Russian state television.

"This will take time too. They have been preparing for this; they know this territory better than us," he added.

Basurin said that separatist forces should aim to blockade the Ukrainian army in the industrial area and "then wait for them to give themselves up."

Basurin estimated that up to 3,500 Ukrainian troops were taking part in fighting at Azovstal and that armed civilians were fighting alongside the Ukrainian army in Mariupol.

"You have to take into account the fact that some residents of Mariupol have taken up arms. Therefore that number could be higher," he said.

Residents have spoken of utter devastation and dire conditions in Mariupol. The city's population has shrunk from 400,000 before the conflict to around 120,000 today.