The United States has halted delivery of equipment related to the stealthy F-35 fighter aircraft to Turkey, marking the first concrete U.S. step to block delivery of the jet to the NATO ally in light of Ankara’s planned purchase of a Russian missile defense system.

U.S. officials told their Turkish counterparts they will not receive further shipments of F-35 related equipment needed to prepare for the arrival of the stealthy jet, two sources familiar with the situation told Reuters on Monday.

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