NATO Supreme Allied Commander Europe (SACEUR), US Army General Curtis Scaparrotti, addresses a news conference at the Alliance headquarters in Brussels, Belgium, Jan. 18, 2017. Photo: Reuters / Francois Lenoir / File.

The top US general in Europe said on Tuesday that he would recommend that the United States should not sell Lockheed Martin Corp F-35 jets to NATO ally Turkey if Ankara does not drop plans to buy S-400 surface-to-air missile defense systems from Russia.

Turkish President Recep Tayyip Erdogan has said it is committed to buying the Russian system, despite warnings from the US-led alliance that the S-400s cannot be integrated into the NATO air defense system.

“My best military advice would be that we don’t then follow through with the F-35, flying it or working with an ally that’s working with Russian systems, particularly air defense systems, with what I would say is probably one of most advanced technological capabilities,” US Army General Curtis Scaparrotti, the head of US forces in Europe, said during a Senate Armed Services Committee hearing. Scaparrotti is also the NATO Supreme Allied Commander Europe.

US officials have said that if Turkey proceeds with the S-400 purchase, Washington will withdraw its offer to sell a $3.5 billion Raytheon Co Patriot missile package.

Last month, Turkish Foreign Minister Mevlut Cavusoglu said Ankara’s purchase of Russia’s S-400 missile defense system was a done deal.