The Pentagon also has started to look at secondary sources to produce parts for F-35s that were being developed in Turkey.
The United States has halted delivery of equipment related to the stealthy F-35 fighter jets to Turkey, a Pentagon spokesman said in a statement on Monday.
The US marked the first concrete step to block delivery of the jet to the NATO ally in light of Ankara's planned purchase of a Russian missile defence system.
"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 Department of Defense spokesman, said in a statement.
The Pentagon said that it had started to look at secondary sources to produce parts for F-35s that were being developed in Turkey.
"Secondary sources of supply for Turkish produced parts are in development. We very much regret the current situation facing our F-35 partnership, but the DoD is taking prudent steps to protect the shared investments made in our critical technology," the statement says.
In recent days, US 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.
Turkish President Tayyip Erdogan has refused to back down from Ankara's planned purchase of a Russian S-400 missile defence system that the United States has said would compromise the security of F-35 aircraft.
Last week, Turkey’s Foreign Minister Mevlut Cavusoglu met with his Russian counterpart, Sergei Lavrov, and said that the S-400 purchase would go ahead.
Cavusoglu at the beginning of March made clear why Turkey is buying Russian S-400 missile defence systems.
"We are buying the S-400s because we couldn’t purchase them [Patriots] from our western allies," asking guarantee the approval of the system by the US Congress.
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 cancelled.
The aircraft is built by Lockheed Martin Corp.
The disagreement over the F-35 is the latest of a series of diplomatic disputes between Washington and Ankara including Turkish demands that the United States extradite Fetullah Gulen, differences over Middle East policy and the war in Syria, and sanctions on Iran.
Ankara insists the extradition of US-based cleric Fetullah Gulen, the leader of Fetullah Terrorist Organization (FETO) the group behind the coup attempt in July 2016 in Turkey that claimed lives of more than 250.
The partnership between Washington and the YPG plays another crucial dispute between Turkey and the US. The group is the Syrian branch of the PKK and is considered as a terrorist organisation by both parties and controls one-third of Syrian territory.
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.
Statement comes ahead of NATO Summit
The US decision on the F-35s seems to complicate Turkish Foreign Minister Mevlut Cavusoglu's planned visit to Washington this week for a NATO summit.
Reuters reported last week that Washington was exploring whether it could remove Turkey from the production of the F-35. Turkey makes parts of the fuselage, landing gear and cockpit displays.
The United States fears the radar on the Russian S-400 missile system will learn how to spot and track the jet, making it less able to evade Russian weapons in the future.
In an attempt to persuade Turkey to drop its plans to buy the S-400, around $2.5 billion, the United States offered the pricier, American-made Patriot anti-missile system in a discounted.
The US announced in March that it approved the possible sale of a $3.5 billion Patriot missile system to Turkey.
Turkey has shown interest in the Patriot system, but not at the expense of abandoning the S-400.
Turkey has engaged with US negotiators in recent days about buying the Patriot system, a person familiar with the matter said on condition of anonymity.
The Patriot system is made by Raytheon Co.
Turkish Defence Minister Hulusi Akar in March said that despite some issues, Turkish pilots were continuing their training at an air base in Arizona on the F-35, each of which costs $90 million, and that Ankara was expecting the aircraft to arrive in Turkey in November.
The US lawmakers also have expressed alarm over Turkey's planned purchase of the Russian system. Four US senators last week introduced a bipartisan bill that would prohibit the transfer of F-35s to Turkey until the US government certifies that Ankara will not take delivery of the S-400 system.