Turkey risks expulsion from the U.S.-led F-35 program, the world’s costliest weapons project, if its government takes delivery of an advanced Russian anti-aircraft system, according to an unclassified summary of a Pentagon report sent to Congress.

Although Turkey “has been an important program partner,” investing more than $1.25 billion in the stealthy F-35 jet since its development phase began in 2002, “the administration will reassess Turkey’s continued participation as one of the eight partner nations should they continue their purchase of the S-400,” according to the two-page summary of a classified report prepared for lawmakers.

“The Turkish government has repeatedly and publicly stated that it has concluded an agreement to procure the S-400” with initial delivery “as early as” July 2019, according to the report seen by Bloomberg News.

In addition to Turkey buying the F-35 built by Lockheed Martin Corp., 10 Turkish companies have been set to produce about $12 billion in parts, including key components such as the center fuselage and some landing gear. For certain items, like the cockpit display, Turkey is the sole source.

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