Russia is planning to begin shipments of S-400 surface-to-air missile systems to Turkey in March 2020, a senior official says of a deal that has raised eyebrows because Turkey is a NATO member.

Sergei Chemezov, head of the Russian state conglomerate Rostec, told the newspaper Kommersant in an interview published on December 27 that the $2.5 billion deal will consist of four batteries of S-400 missiles.

"They are paying 45 percent of the total contract amount as an advance. Fifty-five percent is Russian credit," Chemezov told Kommersant.

Turkey's move to acquire the S-400s has been regarded in some Western capitals as a snub to the NATO alliance amid tensions with Russia over its role in the wars in Syria and eastern Ukraine.

The S-400 deal, first announced by Turkish President Recep Tayyip Erdogan in September, has also caused concern because the Russian-made weapons cannot be integrated into the alliance's defenses.

Turkish Defense Minister Nurettin Canikli said on December 27 that the deal for the missiles had been finalized.

Russia and Turkey support opposing sides in the Syrian war, but Erdogan and Russian President Vladimir Putin patched up their relationship after it was badly damaged when Turkish jets shot down a Russian warplane near the Syrian border in November 2015.

The missiles have a maximum range of 400 kilometers and are capable of reaching targets at a maximum altitude of 30 kilometers.

On December 27, Russian Deputy Prime Minister Dmitry Rogozin said Moscow also expected to sign a deal with India soon on the delivery of S-400s.

Russian officials have also said that Russia and U.S. ally Saudi Arabia are close to signing a deal on supplying the S-400 systems to Riyadh.

With reporting by Kommersant, Reuters, dpa, TASS, and Yenisafak