The U.S. State Department on Monday said it was working with NATO ally Turkey on the possible sale of a Raytheon Co Patriot missile defense system to avert its purchase of a Russian-made S-400 system.
"We are concerned that by purchasing these systems from the Russians, it will be supportive of some of the least good behaviour that we have seen from them," said Tina Kaidanow, acting assistant secretary of the State Department's Bureau of Political Military Affairs.
She added that the US wants to ensure the systems its allies buy "remain supportive of the strategic relationship between us and our allies."
Kaidanow told reporters that U.S. officials were "trying to give the Turks an understanding of what we can do with respect to Patriot."
The US last month warned it could block the delivery of F-35 stealth jets to Turkey if Ankara buys Russia's S-400 system.
Assistant Secretary of Defense Kevin Fahey, the Pentagon's most senior official weapons buyer at the Farnborough Airshow told reporters at the show that "Turkey has had an interest in Patriot, so we've been working for a while how we can make that work."
