The state-run Tass news agency quoted Russia’s defence ministry as saying it had ordered troops to leave the area around the city of Izium in Kharkiv province, to reinforce military operations elsewhere in neighbouring Donetsk.

The announcement came hours after rapidly advancing Ukrainian troops captured the city of Kupiansk, the sole railway hub supplying Russia’s entire frontline across northeastern Ukraine, cutting thousands of Russian troops off from supplies.

After a three-day surge that recaptured dozens of towns and villages held by Russia for months, Ukrainian officials posted photos of their troops raising the country’s blue and yellow flag in front of city hall in Kupiansk.

“To achieve the stated goals of the Special Military Operation for the liberation of Donbass, it was decided to regroup the Russian troops located in the districts of Balakliia and Izium for the purpose of increasing efforts in the Donetsk direction,” Tass quoted the defence ministry as saying.