Russia is reportedly trying to finalize a $2.5 billion deal to supply Turkey with an S-400 surface-to-air missile system that will not integrate with NATO’s system.

Reuters learned that Sergei Chemezov, the head of Russian state conglomerate Rostec, told the Kommersant newspaper that “Russia will supply Turkey with four divisions of S-400 surface-to-air missile divisions for $2.5 billion under a deal that has been almost finalized.”

To the ire of the West, Turkey is moving ahead with the sale although the Russian-manufactured missiles are incompatible with NATO’s system.

“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,” reports Reuters. “Relations between Moscow and the Western military alliance are fraught.”

Chemezov reportedly told Kommersant that Turkey would pay for 45 percent of the deal’s cost up front with Moscow providing loans to cover the rest, notes Reuters.

Russia is expected to begin deliveries in March 2020, revealed Chemezov, noting that Turkey would become the first NATO member to acquire the Russian-made S-400 missile system.

The war against the Islamic State (ISIS/ISIL) has strained the relationship between NATO allies Turkey and the United States, at times placing them on opposite sides of the conflict.

Throughout the anti-ISIS war, the United States has assisted Kurdish forces fighting ISIS in Syria despite Ankara’s repeated accusations that they are terrorists.

Turkey has repeatedly claimed that the U.S.-backed Syrian Kurdish forces are an offshoot of the Kurdistan Worker’s Party (PKK), a group that has been officially designated a terrorist organization by both Washington and Ankara.

However, the United States does not appear to share Turkey’s concerns.

Meanwhile, Turkey and Russia appear to have grown closer despite being on opposing sides of the Syrian conflict. While Russia has backed Assad, Turkey has been lending support to anti-Syrian regime rebels.

Nevertheless, the Assad regime controls the largest portion of Syria, courtesy of support from Russian and Iran, followed by U.S.-allied Kurdish militias who command much of the northern part.

Turkey and Syria share a border.

In a show of appreciation, Assad has willingly allowed Russia to extend its presence in Syria, which is expected to rival U.S. influence in the Middle East.

Support from Russia and Iran made it possible for the struggling Assad forces to turn the tide of the Syrian war in their favor.