ANKARA, Turkey (AP) — Turkish media say Turkey is poised to begin testing Russian-made S-400 air defense systems, despite threats of sanctions from the United States.

The Milliyet newspaper, which has close links to the government, said Monday that the military is planning to test the S-400s that are currently deployed at an airbase in the outskirts of the Ankara.

Turkey took delivery of two Russian S-400 batteries this year, dismissing warnings from the United States that they pose a threat to NATO security. As a result, Washington suspended Turkish participation in the multinational F-35 fighter jet program.

U.S. legislators have warned of sanctions if Turkey activates the system.