Ukrainian forces will continue to fight on even if they are encircled by the Russian advance in the Donbas, Western officials have said.

Following the final fall of the port city of Mariupol, the Russians are seeking to cut off the Ukrainians who have been dug in around the strategically important city of Severodonetsk.

The city is seen as key to the Russians gaining complete control of the Donbas region of eastern Ukraine which has been part-held by pro-Moscow separatist rebels since 2014.

Western officials said that, while superior Russian numbers meant they would eventually succeed in encircling the “Severodonetsk pocket”, that did not necessarily spell defeat for the Ukrainians.

One official said that even if no more aid was able to get through, the Ukrainians had shown they were willing to carry on fighting, inflicting further damage on the Russian military machine.

“I think this largely comes down to political will.

“The Ukrainians don’t want to give up any territory.

“They want to make the Russians fight for very bit of it,” the official said.

“Having those forces continue to fight, they are fulfilling an important military function, degrading the Russian capability to advance and creating time for the Ukrainian forces to continue to improve their defences elsewhere.

“From a loss of life position, escaping might be desirable but from a military point of view and a political point of view the Ukrainians will intend to fight.

“We would expect them to fight for every bit of territory they can.”

The assessment came as President Volodymyr Zelensky issued a renewed call to the international community to step up financial support to his country while continuing to tighten sanctions on Moscow.

In a video address to the World Economic Forum in Davos, he said: “This is what sanctions should be: they should be maximum, so that Russia and every other potential aggressor that wants to wage a brutal war against its neighbour would clearly know the immediate consequences of their actions.”

Meanwhile Western officials played down a call by Lithuania for an international naval coalition to lift the Russian blockade of the Black Sea port of Odesa which is cutting off vital grain exports to the rest of the world.

One official said that, in practice, that could only be achieved with the agreement of the Russians, something which would appear unlikely to be forthcoming.

“I think the thing that we would have to rule out is any sense that this could be done without Russia’s permission,” the official said.

“They have the ability to target both the vessels which move in and out of Odesa and Odesa itself.

“To try and do it without their consent would obviously raise the risk there could be an incident.”