Turkish defense sources said the U.S. bidders, a partnership of Raytheon and Lockheed Martin, recently proposed to Turkey a batch of used Patriot PAC-2 air defense missile systems, deployed in Germany.

“The proposal effectively means some upgrades, and improvements are to be done on the Patriot PAC-2 system which would eventually be replaced by the more advanced PAC-3 system,” one source said. “This would be a government-to-government deal.” The official did not comment on whether Ankara viewed this option favorably.

Since September 2013, Turkey’s defense procurement bureaucracy and industry have been increasingly showing signs of weariness over a potential, $3.44 billion deal with China Precision Machinery Import-Export Corp. (CPMIEC), the front-runner in the competition. CPMIEC is on a U.S. list of companies sanctioned under the Iran, North Korea and Syria Nonproliferation Act.

Turkey has come under strong pressure from its NATO allies since it announced its decision over the T-LORAMIDS. Ankara said it chose CPMIEC’s FD-2000 missile-defense system over rival offers from Franco-Italian Eurosam SAMP/T and Raytheon based on better price and better terms of technology transfer. NATO and U.S. officials have said it will not be possible to integrate any Chinese-built system into the air defense assets that Turkey has in common with NATO and the U.S.