Civilians participate in trench warfare training during a "Test Week" organized by the 3rd Assault Brigade in Kyiv, on Thursday —AFP

Agencies KYIV

Russian forces are slowly tightening the noose around the eastern Ukrainian city of Pokrovsk, a key logistical hub whose main supply lines are under threat nearly three years after Moscow invaded its neighbour.

While Ukraine is stubbornly defending the city, its encirclement or fall could put Russia in a strong position to mount attacks in several directions in the east and increase pressure on Kyiv at a critical juncture in the war.

Inside Pokrovsk, life is bleak. According to the regional governor, 7,000 residents remain out of a pre-war population of 60,000. The last post office recently closed - mail will now be delivered by armoured truck.

On either side of the city, Russian troops are within artillery and drone range of a crucial highway that runs east to west along the entirety of Ukraine, and most cars now take detours along backroads into Pokrovsk for their safety.

Over the past several days, Moscow's forces have reached the main rail line into the city from eastern Ukraine's most important logistical hub, the city of Dnipro. "The situation is generally difficult, the enemy is constantly attacking on foot," said the deputy commander of Ukraine's 59th assault brigade, which is fighting on the Pokrovsk front. He asked to be identified by his military call sign, Phoenix, for security reasons.

The officer said the enemy had much greater numbers of infantry, attacked in small groups willing to take extremely high casualties and adeptly exploited the landscape and low-visibility weather conditions to hide themselves from drones. "Day and night they are moving forwards," Phoenix told Reuters.

Pokrovsk's road and rail connections have made it an important supply centre for a large section of Ukraine's frontline, although in recent months the threat of Russian artillery and drones has limited that function.