Moscow is insisting that the sale of its S-400 missile defense system to Turkey despite harsh US opposition is going “very smoothly” and is “just business.”

"This is a system that the Turkish government wants, and we want to [sell] it,” Viktor Kladov, director for international cooperation and regional policy at the Russian defense firm Rostec told Defense News at a recent defense conference in Abu Dhabi. “We are cooperating with partners and potential partners, regardless of who likes it and who doesn't like it.”

Asked whether Russia will step in with its own offer of Su-35 fighters should the United States retaliate by denying the delivery of F-35s to Ankara, Kladov added, "No, it doesn’t work that way. In the first place, it will be decided by the [Turks].”

Why it matters: The sale of the S-400 has driven yet another wedge into US-Turkey relations. Russia had initially seen the Turkish demand for the Russian air-defense system as a negotiating tactic by Ankara in its bid for the US-made Patriot system. But as talks between Turkey and the United States stalled, Moscow did what it could to make the deal economically and politically viable — both in terms of widening the US-Turkey rift and strengthening its own partnership with Ankara.