WASHINGTON – Two leading senators pressed Secretary of State Michael Pompeo to comply with existing law and impose sanctions on Turkey for purchasing and testing a Russian-made missile system. South Carolina Republican Lindsey Graham and Maryland Democrat Chris Van Hollen said in a letter dated Monday that Turkey’s acquisition of the S-400 anti-aircraft weapons should trigger sanctions under the Countering America’s Adversaries Through Sanctions Act. The two senators cited Turkish and Russian officials who said Turkey isn’t only testing the systems but also has plans for further cooperation with Russia.

The U.S. decision to exclude Turkey from an American-led fighter jet program goes against the “spirit of alliance,” the Turkish government said Thursday, and called on its NATO ally to reverse the decision.

President Donald Trump says the U.S. is not going to sell F-35 fighter jets to Turkey after Ankara decided to buy a missile defense system from Russia.

Turkey hopes to co-produce high-tech weaponry systems with Russia in the future, Turkish President Recep Tayyip Erdogan said, further defying its NATO ally the United States, which has warned the country of possible sanctions over its purchase of a Russian-made missile defense system.

The United States is edging closer to crisis with NATO ally Turkey, now that it has started receiving components of a Russian-made air defense system in defiance of Trump administration warnings