ANKARA: Turkish warplanes shot down an unidentified drone in Turkish air space near Syria on Friday and a United States (US) official said Washington believed it was of Russian origin.

The Russian defence ministry said all of its planes in Syria had safely returned to base and that all its drones were operating "as planned."

The downing of the drone highlights the risks to North Atlantic Treaty Organisation (Nato) member Turkey as Syrian, Russian and US coalition aircraft fly combat missions so close to its borders.

The Turkish military said its jets had shot down the aircraft after it continued on its trajectory despite three warnings, in line with its rules of engagement. Broadcaster NTV said it had come 3 kilometres into Turkish air space.

"It's a drone. We are trying to identify its nationality," a senior Turkish government official told Reuters.

A US official told Reuters that Washington suspected it was a Russian drone, but said the information was still preliminary and declined to give any more details.

Russian jets violated Turkish air space on two occasions earlier this month and Turkey has warned it will respond if the incursions are repeated.

Russia's air strikes in Syria mean that Russian and Nato planes are now flying combat missions in the same air space for the first time since World War Two, heightening concern that the Cold War rivals could fire on each other.

The Russian air force officially informed the Turkish military on Thursday about the violations by Russian jets earlier this month, and about steps it would take to prevent a repetition.

Turkey has also reported unidentified aircraft and Syria-based missile air defence systems harassing its warplanes several times in recent months.