FILE PHOTO: U.S soldiers walk next to a Patriot missile defence battery during join exercises at the military grouds in Sochaczew, near Warsaw, March 21, 2015. REUTERS/Franciszek Mazur/Agencja Gazeta

WASHINGTON (Reuters) - The U.S. State Department has approved a possible $3.5 billion sale of Patriot air and missile defense systems to Turkey, the Pentagon said on Tuesday after notifying Congress of the certification.

The Defense Security Cooperation Agency said the State Department had approved the sale of 80 Patriot guidance-enhanced missiles and 60 other missiles to Ankara along with related equipment, including radar sets, engagement control stations and launching stations.

The State Department said earlier this year it was working with NATO ally Turkey on the possible sale of a Raytheon Co Patriot missile defense system to keep it from buying a Russian-made S-400 system.

But twice in Turkey’s selection process, Ankara passed over the Patriot system, first choosing a Chinese system before turning to the Russian S-400 system in 2017.

U.S. and NATO officials have repeatedly warned Ankara that the Russian system cannot be integrated into the NATO air and missile defense system and that purchasing the S-400 system would jeopardize Turkey’s purchase of Lockheed Martin Corp F-35 fighter jets and possibly result in Washington imposing sanctions.

The notification process alerts Congress that a sale to a foreign country has been approved, but it does not indicate that a contract has been signed or negotiations have concluded.