Russia could also be undermining the economic interests of certain Turkish politicians. Shortly after the incident, the Russian side released a picture showing the 33-year old son of a Turkish leader with two ISIS men. The two sides have very close oil business relations, threatened by Russian bombing.

Prior to the shooting, Russian fighters destroyed the refineries, oil tanks and freight depots controlled by ISIS. That caused a serious damage to the illegal deal between some Turkish businessmen and ISIS.

This Russian argument seems to be more persuasive than Turkey's explanation. What Turkey needs to do is to issue a counter factual explanation that is believable; otherwise, its international image might be seriously undermined.

Another doubt is whether the Turkish side informed the United States of the shooting beforehand. When questioned by Russian foreign minister whether Turkey had got U.S. consent, Turkish foreign minister said neither yes nor no. But it is doubtful Turkey could really dare to down Russian fighter without a strong backing.

And it also sounds very strange that the U.S. DOD issued a statement claiming it had nothing to do with the shooting. It is usual that one party issue the reason why it has done something, but it is rare that one would explain that it has done nothing. All these are doubts, but if the U.S. are really involved, its seriousness in fighting terrorism needs to be questioned.

All in all, the downing of Russian fighter is not founded on solid legitimacy though it might be legal. It seems that before Russia got angry Turkey has already been angry with Russia's military involvement in Syria. But Turkey needs to deliver more persuasive and legitimate reasons for the downing. The legitimacy based on the aircraft of a "friendly" nation crossing the border is certainly not sufficient.

Turkey is always regarded as a responsible regional power. And the world even expects it to play a leading role in fighting against ISIS. Turkey needs to make clarifications about its relations with the terrorist group.

The author is a columnist with China.org.cn. For more information please visit:

http://www.ccgp-fushun.com/opinion/jinliangxiang.htm

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