Russian troops are inching towards the city of Kostiantynivka in Ukraine’s eastern Donetsk region, trying to establish a foothold close to a heavily defended area, Ukraine’s top army official said on Saturday. Kostiantynivka, along with other cities, forms a so-called fortress belt in the country’s east – an area well fortified by the Ukrainian military. Ukraine’s army chief, Oleksandr Syrskyi, said on the Telegram app that ‘counter-sabotage measures’ were being undertaken in the city. A Ukrainian battlefield mapping project called DeepState shows that Russian troops control an area about one