A Russian S-400 surface-to-air missile system. Sergei Malgavko | TASS via Getty Images

WASHINGTON — The United States should not follow through with a multi-billion dollar weapons sale of F-35 jets to Turkey, if Ankara takes delivery of an advanced Russian missile system, the top U.S. military commander for Europe told Congress on Tuesday. "My best military advice would be that we don't then follow through with the F-35, flying it or working with allies that are working with Russian systems, particularly air defense systems," Army Gen. Curtis Scaparrotti, head of U.S. European Command, told members of the Senate Armed Services Committee.

"I would hope that they [Turkey] would reconsider this one decision on the S-400," Scaparrotti said, adding that there could be potential consequences, namely, no future foreign military sales between Washington and Ankara. In 2017, Ankara signed an agreement with Moscow for the S-400 missile system, a deal reportedly worth $2.5 billion. All the while, Turkey has helped finance America's most expensive weapons system, the F-35 Joint Strike Fighter. In short, these two big ticket weapons systems, the S-400 and the F-35, can be used against each other.

An F-35 fighter jet is seen as Turkey takes delivery of its first F-35 fighter jet with a ceremony in Forth Worth, Texas, USA on June 21, 2018. Two such planes destined for Turkey are yet to leave American soil. Atilgan Ozdil | Anadolu Agency | Getty Images

The Russian-made S-400 missile system, which is equipped with eight launchers and 32 missiles, is capable of targeting stealth warplanes like the F-35 fighter. In September, CNBC learned that Turkey began construction of a site for the Russian missile system despite warnings from the United States to not buy the platform, according to a source with firsthand knowledge of an intelligence report. The assessment, published in August, included satellite imagery of a concrete launch facility as well as bunkers, according to the source, who spoke on the condition of anonymity. The new construction fits the pattern for Russia's S-400 surface-to-air missile system, the source indicated. Meanwhile, the State Department has discussed opportunities for Ankara to buy U.S.-made missile defense system. In December, State approved a $3.5 billion sale to Turkey in December for Raytheon's Patriot system.

U.S. Soldiers talk after a routine inspection of a Patriot missile battery at a Turkish military base in Gaziantep, Turkey. Department of Defense photo