Ukraine’s lightning offensive triggered a collapse of some Russian defenses, with Kyiv continuing a rapid advance in the Kharkiv region over the weekend.Russia has likely ordered the withdrawal of its troops from the occupied Kharkiv Oblast west of the Oskil River, the UK ministry of defense said. Ukraine’s top commander Valery Zaluzhnyi said his forces had returned 3,000 square kilometers (1,158 square miles) of lost territory to Ukrainian control since the beginning of September.