Turkey plans to comprehensively test the S-400 anti-aircraft system that the country bought from Russia. Two United States senators (one a Republican, another a Democrat) have appealed to President Donald Trump’s administration to impose sanctions on Turkey because of this.

Republican James Lankford and Democrat Chris Van Hollen, in a communication to the Secretary of State Mike Pompeo, voiced their concerns that Washington’s indecision over this matter has emboldened the Turkish government: “We write concerning public reports that Turkey has activated the radars of its Russian-made S400 anti-aircraft system, to detect US-made F-16 fighter jets returning from the Eunomia exercise conducted by France, Italy, Greece and Cyprus in late August in response to Turkey’s unwarranted aggression in the Eastern Mediterranean. Given this information, we again urge you to impose sanctions on Turkey as required by law”.

Lankford and Van Hollen also asked Pompeo whether Turkey had activated the S-400’s radars to detect the F-16 fighter jets. They also warned Pompeo that if Turkey has integrated the S-400 system into NATO’s system, that might enable Russia to gather information on NATO allies. They asked Pompeo to answer these questions by 14 October.

Turkey bought the S-400 missile system from Russia last year. The US government has stated that Turkey risks US sanctions if it deploys the Russian-made S-400’s but has not imposed any sanctions to date.