KYIV, Ukraine—Ukrainian authorities said their army was closing in on the Russian-occupied city of Kreminna, control of which could allow Kyiv to significantly expand its efforts to retake Russian-held areas in Ukraine’s east. 

Kreminna, a city in the eastern Luhansk region with a prewar population of 18,000, is being abandoned by Russia’s military command as Ukrainian troops advance through the mined and heavily fortified area surrounding it, said Serhiy Haidai, the governor of Luhansk.