Apparently, according to some Turkish media, six Mikoyan MiG-31 Foxhound aircraft have just been delivered to Syria. They form a part of a deal with the Russians which was signed back in 2007 for a total of eight.
BGN News
If the story is true it would appear that the delivery could be in response to the Turkish Government's call for a Syrian no-fly zone, something which Russia is obviously not agreeing with.
It would be interesting to hear views on whether or not the presence of these aircraft in Damascus would alter the idea of a Syrian no-fly zone due to MiG-31 capabilities. Would six, or even eight of this type of aircraft be a game/decision changer, or would they just be a problem that would require 'consideration'.