`` This poses a potential risk to civil aviation as civilian air traffic control can not detect these aircraft or ensure there is no interference with civilian air traffic , '' NATO said in its release . NEW : NATO : More than 19 instances of Russian aircraft in European airspace in 24 hours . Groups of Russian aircraft detected over areas of Baltic , North , Black seas . NATO : ` ` Unusual pattern of air activity over European waters '' Russian official tells CNN the recent flights could be possible prelude to Russian military exercises .
NEW : NATO : More than 19 instances of Russian aircraft in European airspace in 24 hours . Groups of Russian aircraft detected over areas of Baltic , North , Black seas . NATO : ` ` Unusual pattern of air activity over European waters '' Russian official tells CNN the recent flights could be possible prelude to Russian military exercises .