By Maria Kiselyova and Ece Toksabay MOSCOW/ISTANBUL (Reuters) – Six Russian warships are heading to the Black Sea from the Mediterranean for naval drills, the Interfax news agency cited Russia’s Defence Ministry as saying on Tuesday, in what it said was a pre-planned movement of military resources. Russia announced last month its navy would stage a sweeping set of exercises involving all its fleets in January and February, from the Pacific to the Atlantic, in the latest show of strength in a surge of military activity during a standoff with the West over Ukraine. The six ships are scheduled to…