President Tayyip Erdogan's spokesman expressed "unease" on Thursday in a telephone call with U.S. National Security Advisor John Bolton over Washington's decision to remove Turkey from its F-35 programme, broadcaster CNN Turk said. Following the delivery of parts of the Russian S-400 air defence system to Turkey, the United States said on Wednesday it was removing Turkey from the F-35 fighter jet program. Erdogan's spokesman Ibrahim Kalin said relations between the two NATO allies could not remain healthy with such unilateral impositions, CNN Turk reported.