Ankara, Apr 2 ( Prensa Latina ) The United States suspended the delivery to Turkey of F-35 combat aircraft , a first step to block the sale of these aircraft to the country, local media published Tuesday.

Hours earlier Pentagon spokesman Charles Summers said he regretted the adverse situation with Turkey regarding the F-35 program and noted that 'the US Department of Defense is taking prudent measures to protect shared investments in very sensitive technology.

He added that if Turkey were to acquire the Russian S-400 missile defence system. 'Its participation in the F-35 program is at risk.

Turkey joined this project in 2002, and according to official sources, has invested more than 1.25 billion dollars.

However, Summers explained the Pentagon is currently looking for additional suppliers to replace the F-35 components produced in Turkey.

The U.S. announcement also referred to related activities, in reference to the training program that Turkish pilots are currently receiving at Luke's Air Force Base in Arizona.

Since Turkey and Russia completed the transfer of two state-of-the-art S-400 ballistic systems, Washington has launched all sorts of pressures and threats to overturn the agreement, and is eventually focusing on suspending the F-35 program.

Although Ankara plans to acquire 100 of these fighter jets in the coming years, Turkish President Recep Tayyip Erdogan's decision not to cancel the purchase agreed with Moscow has led to increased diplomatic tensions between the United States and Turkey.