A F-35 fighter jet is seen as Turkey takes delivery of its first F-35 fighter jet with a ceremony at the Lockheed Martin in Forth Worth, Texas, United States on June 21, 2018.

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.

The Pentagon confirmed the Reuters report that the equipment delivery had been stopped.

"Pending an unequivocal Turkish decision to forgo delivery of the S-400, deliveries and activities associated with the stand-up of Turkey's F-35 operational capability have been suspended," Air Force Lieutenant Colonel Mike Andrews, a Defense Department spokesman, said in a statement.

Turkish President Tayyip Erdogan has refused to back down from Ankara's planned purchase of a Russian S-400 missile defense system that the United States has said would compromise the security of F-35 aircraft.

The disagreement over the F-35 is the latest of a series of diplomatic disputes between the United States and Turkey including Turkish demands that the United States extradite Islamic cleric Fethullah Gulen, differences over Middle East policy and the war in Syria, and sanctions on Iran.

The sources, who spoke on condition of anonymity, told Reuters the next shipment of training equipment, and all subsequent shipments of F-35 related material, had been canceled. The aircraft is built by Lockheed Martin Corp.

A Pentagon official had told Reuters in March that the United States had a number of items it could withhold in order to send Turkey a signal that the United States was serious about Ankara dropping its ambition to own the S-400.

Turkish officials in Ankara were not immediately available for comment. Turkey has said it will take delivery of the S-400s in July.