U.S. Defense Secretary James Mattis said on Tuesday the United States was concerned about Turkey's purchase of a Russian missile defense system that cannot be integrated into NATO.
The United States has already warned Turkey that it would be subject to sanctions and its purchase of Lockheed Martin fighter jets would be jeopardized if Ankara does not drop plans to purchase the missile defense system.
"Clearly, Turkey bringing a Russian anti-aircraft, anti-missile system into a NATO country -- we cannot integrate that into NATO. Yes, it does concern us and we do not recommend that," Mattis told reporters.
Mattis added Iran has been put on notice, "they will be held accountable for mischief throughout region."
Mattis also said on Tuesday that the United States had recently discussed the use of chemical weapons in Syria with Russia, after media reports that Syria was moving chemical weapons into a rebel-held area the government seeks to recapture.
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"You have seen our administration act twice on the use of chemical weapons," Mattis told reporters. "I will assure you that (the) Department of State has been in active communication, recent active communication, with Russia to enlist them in preventing this ... The communication is going on."