Ukrainian forces were charging through an expanding area of previously Russian-held territory in the east on Friday after bursting through the frontline in a surprise breakthrough that could mark a major turning point in the war. After keeping silent for a day, Moscow effectively acknowledged that a section of its frontline had crumbled southeast of Ukraine's second largest city Kharkiv. "The very fact of a breach of our defences is already a substantial victory for the Ukrainian armed forces," the head of the Moscow-installed administration for occupied areas in Kharkiv province, Vitaly Ganchev, said on Russian state TV.