FILE PHOTO - Moscow - Russia - May 7, 2017 - Russian army S-400 Triumph medium-range and long-range surface-to-air missile system rehearse before the World War II anniversary in Moscow. REUTERS/Maxim Shemetov/File Photo

MOSCOW (Reuters) - Russia will supply Turkey with four batteries of S-400 surface-to-air missiles for $2.5 billion under a deal that is almost complete, Sergei Chemezov, head of Russian state conglomerate Rostec, told the Kommersant daily on Wednesday.

The deal has caused concern in the West because Turkey is a member of NATO but the Russian missile system cannot be integrated into NATO’s military architecture.

In addition, relations between Moscow and the Western military alliance are strained, in part because of Russia’s annexation of Ukraine’s Crimea peninsula.

Turkish Defence Minister Nurettin Canikli said Ankara would purchase two S-400 systems and four batteries and that all agreements were made, the state broadcaster TRT Haber reported.

Turkey will pay 45 percent of the cost up front with Russia providing loans to cover the remaining 55 percent, Chemezov said. Moscow expected to begin the first deliveries in March 2020, he said.

Chemezov told Kommersant that Turkey was the first NATO member state to acquire the advanced S-400 missile system.

He said the Russian and Turkish finance ministries had already completed talks on financing the deal and that the final documents just needed to be approved.