US warns of 'serious consequences' if Turkey activates S-400 system

The United States has expressed to senior levels of the Turkish government that the acquisition of Russian military systems such as the S-400 is unacceptable, the State Department said on Friday, warning of "potential serious consequences" for its security relationship with Turkey if it activates the system.
"If confirmed, we would condemn in the strongest terms the S-400 test missile launch as incompatible with Turkey’s responsibilities as a NATO  Ally and strategic partner of the United States," State Department spokeswoman Morgan Ortagus said in a statement.