In a fresh setback for the Ukrainian army, troops have been forced to retreat from the airport in the eastern city of Luhansk, under attack, Kyiv claims, from a Russian tank battalion.

Over recent days, Ukraine’s forces have suffered a run of reverses on the battlefield in the Luhansk and Donetsk areas. Pro-Russian separatists are also pushing towards the port city of Mariupol.

Until last week, Ukraine had appeared close to crushing the four-month rebellion in the east. Kyiv now believes Russian forces are helping the rebels to turn the tide of the war.

Confirming that Ukrainian soldiers had been ordered to leave Luhansk airport, military spokesman Andriy Lysenko said: “Looking at the precision of the shelling, we can say it was carried out by professional artillery gunmen of the Russian armed forces.”

Moscow denies the presence of Russian tanks and troops in Ukraine, despite what NATO and Western governments have said is overwhelming evidence to the contrary.