When Russian and US jets came into close proximity over Syria early last month, the Pentagon and the White House were swift to condemn.

"Wreckless" and "irresponsible" were just some of the stiff words they used at the time.

But now that Turkey has actually shot a Russian jet down, there is a tangible reluctance to up the ante, and a scramble to lower the temperature.

Caution is the name of the game, with the Pentagon spokesman, Peter Cook, still saying that the US cannot definitively conclude that Turkish airspace has been compromised.

As a Nato member, Turkey will expect the US and others to back its actions; but with Russia crucial to the prospects of pushing forward a political solution in Syria, de-escalation is the watch word on everyone's lips.