Group's aid for Turkey also meant to prevent Russia clash

NATO plans to send air defence support to Turkey partly to minimise the risk of Ankara shooting down another Russian warplane while assuaging its fears of a spillover from the conflict in Syria, senior alliance sources say.

The mission, expected to be approved by the Western defence alliance's council on Friday, has been under preparation for 10 months, long before the incident with Russia, and NATO Secretary General Jens Stoltenberg has said it is not linked.

But NATO sources said the shooting down had galvanised allies to come forward with more support and tailor the assistance to help lower tensions between Moscow and Ankara by taking a role in managing Turkish airspace.

"NATO rules of engagement are more cautious than those of Turkey," said one NATO source.

While the U.S.-led alliance publicly backed Turkey after its fighters downed a Russian bomber that strayed into its airspace from Syria on Nov. 24 in the first such incident since the Cold War, several allies were privately alarmed and urged restraint.

Stoltenberg said strengthening air defences for Turkey, which has long expressed alarm over the civil war raging near its border, was a commitment that went back well before the shooting down of the Russian plane.

The package, set to be approved without debate, includes interceptor aircraft, Airborne Warning and Control System (AWACS) radar planes and a naval unit with command ships and frigates with anti-ship and anti-aircraft missiles.

It will have a dual function of defending Turkey while contributing to a U.S.-led coalition air campaign against Islamic State in Syria and Iraq. But the NATO presence may also act as a soft constraint on Ankara.