Ukraine's military has pulled its forces back from defending a vital airport in the east against what is decribed as a column of Russian tanks, as President Petro Poroshenko accused Moscow of "direct and open aggression".
Russia's War Against Ukraine
Al Jazeera: Ukraine’s troops retreat from vital airport
Ukrainian troops ride on a tank and a self-propelled gun near the eastern city of Luhansk on Aug. 20, 2014.
