Moscow and Ankara maintain contacts on the issue of the S-400 missile systems Turkey has bought from Russia, Russian Ambassador to Turkey Sergey Vershinin said. The Russian always responds with understanding to the requests from our partners, including Turkey. Turkey purchased four S-400 anti-aircraft missile battalions from Russia in 2017 under a $2.5 billion contract. In October 2019, Russia’s arms exporter Rosoboronexport (part of the state tech corporation Rostec) announced that the contract for the systems had been fulfilled. Following the signing of the contract between Turkey and Russia for the supply of a regimental set of S-400 systems, Ankara was excluded from the US program to develop the next-generation F-35 fighter jet.