Sharjah24 - Reuters: Ukrainian soldiers resisted a Russian ultimatum to lay down arms on Sunday in the pulverised port of Mariupol, which Moscow said its forces had almost completely seized in what would be its biggest prize of the nearly two-month war.

Ukrainian Prime Minister Denys Shmyhal said troops in Mariupol were still fighting despite a Russian demand to surrender by dawn.

"The city still has not fallen," he told ABC's "This Week" programme, adding that Ukrainian soldiers continue to control some parts of the city.

Russia said on Saturday it had control of urban parts of the city, with some Ukrainian fighters remaining in the Azovstal steelworks overlooking the Sea of Azov.

Capturing Mariupol, the main port in the southeastern region of Donbas, would be a strategic prize for Russia, connecting territory held by pro-Russian separatists in the east with the Crimea region that Moscow annexed in 2014.

After failing to overcome Ukrainian resistance in the north, the Russian military has refocused its ground offensive on Donbas while maintaining long-distance strikes elsewhere including the capital, Kyiv.