Kyiv’s forces are close to encircling a large concentration of Russian troops in eastern Ukraine in what would be a fresh blow to Moscow in the wake of its unpopular mobilisation and declared annexation of four Ukrainian provinces.

After a lightning counter-offensive this month that liberated thousands of square kilometres in Kharkiv, Ukrainian units have pushed further east, alarming military bloggers and nationalist commentators in Moscow. By Friday they had almost surrounded the town of Lyman in north-east Donetsk, one of the provinces annexed by Russia.

Lyman is a key staging ground for Russian forces in their campaign to capture the rest of Donetsk province. Ukrainian forces are advancing from three directions on the town — west, north and south — and are looking to trap potentially several thousand Russian troops there.

Ukraine’s main objective could be to attack Svatove, a town to the north of Lyman, has become an important logistics hub for Russian forces after the Kharkiv counter-offensive, said Mykhailo Samus, director of the NewGeopolitics Research Network in Kyiv and a former Ukrainian military officer.

‘If the Russians lost Svatove it would be a disaster for them, especially if [the] Ukrainian offensive continues further east to liberate that part of Luhansk Oblast [province],” Samus added.

He said that as many as 5,500 Russian troops could now be surrounded in the

Lyman area.