"We have received a letter from the Turkish government requesting the continuation of the Patriot mission," a NATO official told AFP on condition of anonymity.

"The North Atlantic Council has regularly assessed the situation and the implementation of the Patriot mission. It is clear that the overall risks and threats to Turkey remain serious," the official said.

A Turkish foreign ministry diplomat, contacted by AFP, also confirmed Ankara's request.

Turkey turned to its NATO allies after a mortar bomb fired from Syrian territory killed five Turkish civilians in the border town of Akcakale in October last year.

Since the deadly attack, Turkey has retaliated in kind for every Syrian militants’ shell that has landed on its soil and beefed up its volatile 910-kilometre (560 mile) frontier.

Washington confirmed that Turkey has asked NATO "to continue to augment its air defense capabilities to aid in the defense of its population and territory."

"We look forward to working through NATO to address the request," State Department spokeswoman Jen Psaki said, adding that "we respect and value Turkey as a long-standing NATO and US ally."

Without specifying whether Washington would agree to the demand, Psaki added the US did "recognize the needs they have."

The six batteries of the US-made missiles, effective against aircraft and short-range missiles and dispatched by the Netherlands, Germany and the United States, are deployed in the southern city of Adana and the southeastern cities of Kahramanmaras and Gaziantep.

NATO approved their initial deployment in December.

But Russia opposed the Patriot deployment, fearing that it could spark a regional conflict also drawing in NATO.

NJF/NJF