Ukraine said on Sunday that its forces were working to take control of towns and villages around the strategic hub of Izyum from Russian troops as part of the counter-offensive in the country's east.

"Our forces entered Kupiansk. The liberation of settlements in the Kupiansk and Izyum districts of the Kharkiv region is ongoing," the Ukrainian military stated in a general update on Sunday.

There has been no response from the Russian side.