Ukraine's top military commander has admitted his soldiers are facing difficult conditions defending Pokrovsk - a key eastern front-line town - against massed Russian forces.

Gen Oleksandr Syrskyi said Ukrainian troops were fending off a multi-thousand enemy force - but denied Russian claims that they were surrounded or blocked.

He confirmed that elite special forces had been deployed to protect key supply lines which, army sources said, were all under Russian fire. The defense ministry in Moscow reported that Ukrainian troops were surrendering and 11 of their special forces had been killed after landing by helicopter - something denied by Kyiv.

Gen Syrskyi said in a social media post on Saturday that he was back on the front to personally hear the latest reports from military commanders on the ground in the eastern Donetsk region. In a short video, Syrskyi is seen studying battlefield maps with other commanders, including the head of Ukraine's military intelligence, Kyrylo Budanov.

It is unclear when or where the footage was recorded. Ukrainian media earlier reported that Budanov was in the region to personally oversee the operation by the special forces.

The deployment of special forces suggests officials in Kyiv are determined to try to hold on to the town, which Russia has been trying to seize for more than a year. Ukraine's 7th Rapid Response Corps said on Saturday that Ukrainian troops have improved [their] tactical position in Pokrovsk - but the situation remained difficult and dynamic.

Late on Friday, Ukrainian President Volodymyr Zelensky stressed that the defense of Pokrovsk was a priority. There have been growing reports of Russian advances around the strategic town to the west of the Russian-seized regional capital of Donetsk.

Images shared with news agencies late on Friday appear to show a Ukrainian Black Hawk helicopter deploying about 10 troops near Pokrovsk, although the location and date of the footage could not be verified. Russia's defense ministry said it had thwarted the deployment of Ukrainian military intelligence special forces north-west of the town, killing all 11 troops who landed by helicopter.

A military source in Donetsk told the BBC that Ukrainian forces were not surrounded but their supply lines were under fire from Russian troops. The US-based Institute for the Study of War said Ukrainian forces had marginally advanced during recent counter-attacks north of Pokrovsk, but that the town was mainly a contested 'grey zone'.

Pokrovsk is a key transport and supply hub whose capture could unlock Russian efforts to seize the rest of the region. But Kyiv also believes its capture would help Russia in its efforts to persuade the US that its military campaign is succeeding - and, therefore, that the West should acquiesce to its demands. Washington has grown increasingly frustrated with the Kremlin's failure to move forward with peace negotiations.