Echoing other American and North Atlantic Treaty Organisation officials who have advised against the purchase of the Russian weapons, the top USA general cautioned that the surface-to-air missile defense system would be present a threat to the F-35, noting that it is not compatible with other allied systems and would ultimately threaten security.
Turkey's military relationship with the United States will face serious consequences if Ankara takes possession of the Russian S-400 air defence system, Defence Department spokesperson Charlie Summers told reporters on Friday.
In an interview with Kanal 24 television late Wednesday, Erdogan also said Turkey could consider purchasing the more advanced Russian S-500 system in the future.
Erdogan said Turkey could still purchase the Patriot missile defence system "if the conditions are suitable, the prices are suitable (and) if we can conduct a joint production". "So I would hope they would reconsider this one decision on S-400 - one system - but potentially forfeit numerous other systems and... one of the most important systems that we can provide".
"My best military advice would be that we don't then follow through with the F-35, flying it or working with allies that are working with Russian systems, particularly air defense systems", Army Gen. Curtis Scaparrotti said Tuesday.
The US fears the Russian system could be used to collect intelligence on the jet's stealth capabilities, but Erdogan said "we've researched it, there is no such thing". They have warned Ankara that Turkey risked both jeopardising its purchase of Lockheed Martin F-35 jets from the USA and having sanctions imposed.
Turkey, the country with the longest land border with Syria which is considered to be a "failed state", a neighbor to the newly recovering Iraq, as well as having continental shelf problems with economically bankrupt Greece, still does not have an air defense system.
Some have said the USA is concerned that the S-400 poses security risks to the F-35 Joint Strike Fighter project.
"I would say first of all if they accept the S-400 and to establish it within Turkey, there's first of all an issue that it's not interoperable with North Atlantic Treaty Organisation systems nor is it interoperable inside our integrated air defense system so that presents one problem", Scaparrotti said. Ankara insists the S-400 offers the best value for its needs and poses no threat to North Atlantic Treaty Organisation systems.
The US agreed to sell 100 of its F-35 fighters to Turkey in December and has so far delivered two of the aircraft. Congress a year ago ordered a delay in future deliveries.