Turkey is in the process of constructing a site for a Russian missile system despite warnings from the US to not buy the platform, according to a source with firsthand knowledge of an intelligence report covering the subject, CNBC reported.

The assessment, published a month ago, 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, all of that comes as Congress is inching closer to blocking the transfer of two F-35 jets to Turkey.

In June, the U.S. defense giant held a formal hand-off ceremony at its F-35 facility in Fort Worth, Texas. After the ceremony, Lockheed ferried the aircraft to Luke Air Force Base in Arizona where Turkish pilots began training alongside U.S. airmen.