LVIV, Ukraine (Reuters) – The mayor of Ukraine’s front line city of Kharkiv on Monday said the city had been under constant attack by Russian forces, who had fired at central districts causing an unspecified number of casualties. “They’re firing at us constantly,” Mayor Ihor Terekhov said on national television. (Reporting by Natalia Zinets; Writing by Alessandra Prentice; Editing by Hugh Lawson)