Turkey has signed a deal with Russia to buy S-400 missile defence systems, its first major weapons purchase from Moscow, in an accord that could trouble Ankara's NATO allies.
The purchase of the surface-to-air missile defence batteries, Ankara's most significant deal with a non-NATO supplier, comes with Turkey in the throes of a crisis in relations with several Western states
Moscow also confirmed the accord, with Vladimir Kozhin, Mr. Putin's adviser for military and technical cooperation, saying the contract has been signed and is being prepared for implementation
The purchase of the missile systems from a non-NATO supplier is likely to raise concerns in the West over their technical compatibility with the alliance's equipment.
Turkey - which has the second largest standing Army in NATO after the United States - was free to make military acquisitions based on its defence needs.
Moscow would extend a credit to Turkey for the purchase of the weapons.
However signing the deal does not mean that delivery is imminent, with Russia facing a high demand for the S-400s from its own armed forces and key clients like China and India.
Some analysts have suggested the message sent to the West by the military cooperation between Moscow and Ankara is as important as the delivery itself.
In 2015, Turkey scrapped a $3.4 billion deal with China to build its first anti-missile system.
Russia's relations with NATO have been in crisis over its annexation of Crimea from Ukraine and for backing pro-Moscow separatists in eastern Ukraine.
Turkey, a NATO member since 1952, has currently troubled ties with the United States over a number of issues including Washington's support for the People's Protection Units (YPG) Syrian Kurd militia which Ankara considers a terror group.