NEW : NATO : April : 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 . The US is not going to let this go on much longer and will have to take some sort of action against Russia if it wants the world to believe that they are serious about stopping this. NATO official tells CNN the recent flights could be possible prelude to Russian air 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 . The US is not going to let this go on much longer and will have to take some sort of action against Russia if it wants the world to believe that they are serious about stopping this. NATO official tells CNN the recent flights could be possible prelude to Russian air exercises .