Russian military analysts list Sloviansk, Kramatorsk, Druzhkivka and Kostiantynivka as the "fortress cities" in Ukraine's east accessible from Chasiv Yar if Moscow's forces can get there, something Kyiv is determined to stop.

Russia said on Thursday it had captured the town of Chasiv Yar in eastern Ukraine after nearly 16 months of fighting, opening the way for potential further advances. Russia's Defence Ministry said in a brief statement its forces had "liberated" the town.