The warning comes amid soaring tensions with the Nato-member country after Moscow claimed it has removed a Polish flag from a memorial site commemorating the killing of thousands of Poles in the Soviet Union. Russia's defence ministry says its troops have killed "up to 80" Polish fighters in "precision strikes" in the eastern Donetsk region. It said in a statement: "Up to 80 Polish mercenaries, 20 armoured combat vehicles and eight Grad multiple rocket launchers were destroyed in precision strikes on the Megatex zinc factory in Konstantinovka". And the mayor of Smolensk, where the Polish flag was removed Andrei Borisov,...