Turkey’s security bureaucracy already has alternative plans in case the United States halts the delivery of the F-35 jets over Ankara’s decision to buy S-400 missile systems and has been considering Russian Su-57 or Chinese J-31 stealth fighters as possible options, pro-government Yeni Şafak daily said on Sunday.

As a last move of Washington’s increased pressure on Ankara to cancel the S-400 deal with Moscow, the Acting U.S. Secretary of Defense Patrick Shanahan sent a letter to Turkish Defence Minister Hulusi Akar on Thursday detailing how Turkey’s participation in the F-35 program will be all but suspended as of July 31, unless Turkey withdraws from its planned purchase of Russian defence systems.

In April, the United States froze a joint F-35 manufacturing program with Turkey, which produces 6-7 percent of the parts for the fighter jets, while there is a bipartisan support in U.S. Congress to halt the delivery of 100 F-35 jets Turkey plans to buy from the United States, in case Ankara goes ahead with S-400 acquisition plans.

CNBC reported last month that Washington had told Ankara to decide by early June to either cancel its acquisition of Russia’s S-400 missile systems and buy U.S.-made Patriots or risk expulsion from an advanced U.S. fighter jet program, U.S. sanctions and possible blowback from NATO.

According to Yeni Şafak, the Pentagon made its last move by sending the letter on Thursday, a day before the end of the deadline set for June 7.

Ankara prioritises S-400s over F-35 fighter jets as the missile systems are seen as an urgent need due to regional tensions, the daily said.

“The B, C, D plans are ready in case the F-35 project goes to the dump after S-400 purchase,” Yeni Şafak said. Turkey will sustain its air force by increasing the maintenance of existing aircrafts, while it will escalate efforts to produce its own jets, according to the pro-government newspaper.

“To sit at the table with Russia for the acquisition of military aircraft is among the options. The security bureaucracy is also exploring Chinese J-31s, along with Russian Su-57s,” it said, adding that those options were also more cost-effective compared to F35s.

“Ankara already thinks that even if F-35s are delivered, they will create serious security risks for Turkey as they are directly commanded by the United States. Therefore, nobody regrets ‘losing’ F-35s,” the daily said.

Mehmet Barlas, a columnist of the pro-government daily Sabah, on Sunday also suggested immediately ordering Russian jets, without waiting for U.S. sanctions that can be imposed under the Countering America's Adversaries Through Sanctions Act (CAATSA).

Tyler Rogoway and Joseph Trevithick said in an article they penned for The Drive automotive website last month that Moscow had stated it had been ready to work with Turkey on the export and production of their Su-57 advanced fighter jet to fill the void of the U.S.-produced F-35s.

Turkish Foreign Minister Mevlüt Çavuşoğlu said in April that Turkey could buy aircrafts elsewhere, when asked about Ankara’s possible expulsion from the F-35 programme.

“There are (Russian) Su-34, Su-57 and others. I will absolutely meet my needs from somewhere until I can produce it myself,” Çavuşoğlu said.