The US has threatened to strip Turkey of its participation in the F-35 program, and promised that it would not deliver the advanced new fighter jet to Ankara unless it pulls out of its S-400 air defence system deal with Russia.

Turkey's security bureaucracy is actively considering buying Russian and Chinese made fifth-generation fighter aircraft if the Turkish deal with Washington on the purchase of 100 F-35s falls through, Yeni Safak, one of Turkey's most influential pro-government newspapers, has reported.

According to the outlet, "plans B, C, and D" have already been prepared "in the event that the F-35 project is dumped following the S-400 purchase."

These plans reportedly include the acceleration of the Turkish defence ministry's efforts to develop a homegrown fighter aircraft, talks with Russia about the supply of Sukhoi's new fighter jet design, the Su-57, and consideration of the Shenyang FC-31 (aka the J-31), China's new stealth multirole fighter platform.

"These aircraft stand out with their low cost compared to the F-35, each of which costs approximately $100 million," Yeni Safak noted. Furthermore, "Ankara already thinks that even if the F-35s are delivered, they will create serious security risks for Turkey, as they are directly commanded by the US. Therefore, nobody regrets 'losing' the F-35s," the paper stressed.

Last month, Rostec Corporation reiterated Russia's willingness to explore the possibility of selling the Su-57 to Turkey if Ankara's deal with Washington on the F-35 were to fall through. Earlier this year, an aviation industry source said that the Su-57 has already attained an export permit. In April, Turkish Foreign Minister Mevlut Cavusoglu warned that Ankara would satisfy its need for advanced fighter jets "in another place" if Washington scrapped its commitment to sell Turkey the F-35.

US Acting Defence Secretary Patrick Shanahan has given Turkey until July 31 to back out of its S-400 deal with Russia, warning that Washington would suspend Ankara's involvement in the F-35 program if it goes through with the purchase of the Russian-made air defence system.

Last week, Shanahan sent a letter to Turkish counterpart Hulusi Akar, warning him that although the US seeks "to maintain our valued relationship, Turkey will not receive the F-35 if Turkey takes delivery of the S-400." Earlier, the US threatened Turkey with a series of measures, including sanctions, if it didn't back out of its deal with Moscow.

On Monday, Turkish Defence Industries Directorate chief Ismail Demir confirmed that the United States had not replied to Turkey's proposal to create a joint working group to discuss the threat to US systems allegedly posed by the S-400s, reiterating that the S-400 issue was "closed."

Russia and Turkey signed a $2.5 billion contract for four battalion-sets' worth of S-400s for Ankara in late 2017. Deliveries are expected to start in July.