WASHINGTON — A messy multibillion-dollar deal between Turkey and the United States took another turn over the weekend as Moscow announced it was in the process of delivering a much-anticipated missile system to Ankara.

The delivery of the Russian-made S-400, a mobile surface-to-air missile system, is said to pose a risk to the NATO alliance as well as the F-35, America's most expensive weapons platform.

Turkey, a NATO partner, faces several consequences for accepting the Kremlin's missile system, including economic sanctions and removal from the supply chain for the F-35.

"We underscore that Turkey will face very real and negative consequences if it completes its S-400 delivery," a U.S. State Department official told CNBC. "NATO countries need to procure military equipment that is interoperable with NATO systems. A Russian system would not meet that standard." The official, who declined to be named, said that NATO allies and the U.S. have offered Turkey other missile platforms.

The Pentagon and White House did not immediately respond to CNBC's request for comment.

In 2017, Ankara brokered a deal reportedly worth $2.5 billion with the Kremlin for the S-400 despite warnings from the U.S. that buying the system would come with political and economic consequences.

The S-400, the successor to the S-200 and S-300 missile systems, made its debut in 2007. Compared with U.S. systems, the Russian-made S-400 is believed to be capable of engaging a wider array of targets, at longer ranges and against multiple threats simultaneously.