The purpose of US sanctions against Turkey for the purchase of S-400 anti-aircraft missile systems (SAM) is in fact Russia. This is stated in a statement published on the website of the US Department of State.
The text notes that the sanctions were introduced in accordance with paragraph 231 of the Countering America's Adversaries Through Sanctions Act (CAATSA). “Today's actions are not aimed at undermining the military capabilities or combat readiness of Turkey or any other US ally or partner, but rather to make Russia pay for a wide range of its harmful actions,” the publication said.
On December 14, Washington imposed sanctions on Ankara. They hit the staff of the Turkish defense department and officials, in particular, the head of the secretariat of the Turkish defense industry Ismail Demir, other employees of the department, as well as three other individuals.
Deliveries of the S-400, which caused a crisis in relations between Turkey and the United States, began in mid-July 2019. Washington demanded to abandon the deal and purchase American Patriot complexes in return, threatening to delay or even cancel the sale of the latest F-35 fighters to Turkey.