Heavy fighting is raging in Ukraine's eastern Donbas region where Russian forces have stepped up their bombardment beyond the frontlines, the UK's Ministry of Defence has said.

Moscow faces stiff Ukrainian resistance to its effort to encircle the area around the city of Sievierodonetsk and consolidate Russian control of the Luhansk region - the main focus but not the only Russian effort in the campaign to capture the Donbas, the ministry said.

Cities not under Russian control have been constantly shelled and one Ukrainian official said Russian forces targeted civilians trying to flee.

Russia is bent on capturing the eastern industrial heartland of coal mines and factories and has made some localised gains, the MoD said in its daily intelligence briefing, but Ukraine's long-established Joint Force Operation probably retains effective command and control of that front.

To the north in Ukraine's second-largest city, Kharkiv, residents lined up for rations of tea, sugar, pasta and cereal, holding out plastic bags to receive cups of flour and other supplies.

An aid worker said many had fled the city while it was under siege and returned, lacking a regular income and the means to feed their families without help.

Kherson, a region bordering Donetsk to the east and Crimea to the south, was taken by Russian forces early in the war.

An official there said the region's pro-Kremlin administration will ask Moscow to set up a military base there.

"We will be asking for it, the entire population is interested in it. It is vitally important and will become a security guarantee for the region and its residents," said Kirill Stremousov, deputy head of the Russia-installed administration in Kherson.

Meanwhile, workers digging through rubble have found 200 bodies in Mariupol, Ukrainian authorities said - another grim discovery in the ruined port city that has seen some of the worst suffering of the three-month-old war.

The bodies found in the basement of a collapsed apartment building were in a state of decomposition and a stench permeated the area, said Petro Andryushchenko, an adviser to the city's mayor.

Mariupol, which the Russians recently claimed full control over, became a worldwide symbol of defiance for the diehard defence put up for months by fighters at the Azovstal steelworks.

The announcement of the discovery of the bodies came shortly after Ukrainian President Volodymyr Zelensky accused Russia of waging "total war", seeking to inflict as much death and destruction as possible on his country.

Ukrainian officials have speculated Russia plans to stage a referendum in the region to declare its independence, similar to ones held in Donetsk and Luhansk regions in 2014.

Moscow recognised the self-proclaimed Donetsk and Luhansk republics two days before invading Ukraine, using that as a pretext to send troops to its ex-Soviet neighbour.

Mr Stremousov denied such plans earlier this month and said the region will ask the Kremlin to make it part of Russia instead.

Kremlin spokesman Dmitry Peskov has said it is up to the people of Kherson to decide how and where they want to live.

Meeting in Tokyo with fellow leaders in the Indo-Pacific security coalition known as the Quad, President Joe Biden said on Tuesday that Russia's war in Ukraine had brought a "dark hour in our shared history".

Global defence leaders on Monday agreed to send more advanced weapons to Ukraine, including a Harpoon launcher and missiles to protect its coast, Defence Secretary Lloyd Austin told reporters.

Mr Zelensky has called for "maximum" sanctions against Russia, with an embargo on Russian oil, a complete cut-off of trade and withdrawal of foreign companies, in a video address to the World Economic Forum in Davos, Switzerland.

Later, in his evening address to the nation, Mr Zelensky said four missiles had killed 87 people last week in the town of Desna, 34 miles north of Kyiv, in one of the deadliest single strikes in the war.

Also on Monday, a Ukrainian court sentenced a captured Russian soldier, Sergeant Vadim Shishimarin, 21, to the maximum penalty of life in prison for killing a civilian.

He was sentenced for shooting a 62-year-old man in the head in a village in the north-eastern Sumy region in the opening days of the war. His lawyer indicated he may appeal.