The US is deeply concerned with reports that Turkey is continuing its efforts to bring the S-400 into operation, a State Department official has said.Responding to a press report on Hellas Journal website, the official noted that “we are deeply concerned with reports that Turkey is continuing its efforts to bring the S-400 into operation. We have taken tangible steps in response to Turkey’s receipt of the system by unwinding Turkey’s participation in the F-35 program.”Moreover he said that “we …








