By Aleksandar Vasovic KYIV (Reuters) -Russia warned Kyiv residents to flee their homes on Tuesday and rained rockets on the city of Kharkiv as Russian commanders intensified their bombardment of Ukrainian urban areas in a shift of tactics after their six-day assault stalled. A U.S. official said a miles-long armoured column bearing down on the capital Kyiv had not made any advances in the past 24 hours, frozen in place by logistics problems, short on fuel and food, and perhaps pausing to reassess tactics. Russia’s defence ministry said its forces would strike targets in Kyiv used by Ukraine’s …