The White House and the Pentagon will be torn on how to react to the downing of the Russian fighter jet.

On the one hand, Washington will want to stand by a Nato ally.

America's military does not want to upset Ankara and jeopardise its access to the vital Turkish airbase at Incirlik.

But on the other hand, the White House will judge that Turkey over-reacted.

It is clear that the Russian planes are not a direct threat to Turkey.

Syria has now become the perfect strategic storm: dragging in all the Great Powers and regional actors; multiple proxy wars playing out on the ground; misjudgments by pilots triggering dangerous clashes; and no end in sight for a conflict fuelling the world's most dangerous terrorist groups.

US diplomats have long been close to despair over Syria.

Now the American military will also be profoundly alarmed by a conflict that keeps getting more complicated and now threatens to spiral out of all control.