Washington vehemently opposes Ankara's deal with Moscow on the procurement of S-400s, threatening to suspend the delivery of F-35s to Turkey under pretext that the Russian system would allegedly reveal the top jet’s weaknesses to Moscow.

Acting US Defence Secretary Patrick Shanahan announced during a House of Representatives Armed Services Committee hearing that the US wants Turkey to remain in the F-35 programme and thus needs to convince Turkey to buy Patriot air defence systems.

"We absolutely do [need Turkey in F-35 programme]. We need Turkey to buy the Patriot", he said.

An S-400 anti-aircraft missile system during the preparation of military equipment for the military parade marking the 73rd anniversary of the victory in the Great Patriotic War, in Kaliningrad ©
Sputnik / Igor Zarembo US 'Reconciling' Presence of Russia-Made S-400, F-35 in Turkey - Top General

Shanahan was possibly suggesting that by doing so, Ankara would drop the S-400 deal with Russia that sparked tensions between Turkey and the US. Despite being NATO allies, the two countries don't see eye to eye on Turkey's air defences. After unsuccessful attempts to obtain US-made Patriots, Ankara looked for other options and struck a deal with Moscow in December 2017, prompting criticism from Washington.
The latter suggested that the S-400 systems could compromise the soon-to-be-delivered F-35 jets, revealing their specifications and weaknesses to Russia. US lawmakers have initiated attempts to halt F-35 deliveries to Turkey unless it drops the S-400 deal. Later, the US State Department also finally gave a green light to sell Patriot systems to Turkey.
Ankara has repeatedly refused to drop the deal with Moscow, demanding that the F-35s, which Tukey has already paid for and helped to produce, be delivered on time. Turkey has also expressed willingness to buy Patriot systems if the deal was good enough, but only in addition to the S-400s, despite US remarks that the two systems are incompatible. READ MORE: US Wants to 'Send Signals' to Turkey on F-35 Supplies Amid S-400 Spat — Report
Recently, Katie Wheelbarger, acting assistant secretary of defence for international security affairs, revealed that Washington is planning to send "send signals" to Ankara, hinting at a possible freeze of preparations for the delivery of F-35s and relocating the production of certain parts of the jet from Turkey to Europe.Source: sputniknews.com