By Ece Toksabay and Maria Tsvetkova
ANKARA/MOSCOW (Reuters) - Turkey has rejected a Russian request for a routine observation flight over its territory under a decade-old pact meant to enhance mutual confidence, a move Moscow said set "a dangerous precedent".
Russia and NATO member Turkey back opposing sides in Syria's civil war, with Moscow supporting President Bashar al-Assad, while Ankara supports rebel fighters battling to overthrow him.
Relations between Moscow and Ankara have deteriorated sharply since Nov. 24, when Turkey shot down a Russian fighter jet near the Syrian border, saying it had violated its air space. Russia denied any incursion.
Under a 1992 treaty allowing signatories to conduct aerial observation on each other's territory to promote transparency in military affairs, Russia had been scheduled to conduct its latest flight over Turkey between Feb. 2-5.
But Turkey's foreign ministry said on Thursday an agreement could not be reached and the flight did not occur.
Russia blamed Turkey, saying Ankara had not set any conditions for the proposed observation flight, but that when Moscow proposed a route which included surveillance of Turkish regions bordering Syria, it was rejected.
"In this way, as a result of the violation of the terms of the treaty and Turkey's unconstructive actions, a dangerous precedent has been set for uncontrolled activities by one of the signatories of the Open Skies treaty," Russian defence ministry official Sergei Ryzhkov said.
The Turkish foreign ministry said observation flights only take place when both sides can agree the mission plan, pointing out that Russia imposed limitations on flights over its territory.
Last Saturday, Turkey said another Russian jet had violated its airspace, again denied by Moscow.
The Treaty on Open Skies, negotiated in 1992 by then-members of NATO and the Warsaw Pact, was established to allow its 34 signatories to conduct aerial observation on each other's territory in a bid to promote transparency in military affairs.
Turkey's agreement with Russia went into effect in 2006, and since then Moscow has conducted an average of two observation flights over Turkey each year, and Turkey four a year over Russia, according to the Turkish military.
Assad's forces, backed by Russian air strikes, have advanced on the rebels north of the Syrian city of Aleppo in recent days, choking opposition supply lines from Turkey and contributing to the collapse of U.N.-backed peace talks in Geneva on Wednesday.
Russia has imposed economic sanctions on Turkey in response to the downing of its jet, one of the worst diplomatic ruptures between a NATO member and Russia in years, a standoff which has complicated international efforts to fight Islamic State.
(Writing by Dasha Afanasieva; Editing by Nick Tattersall and Raissa Kasolowsky)