With few other options at its disposal, Washington has been forced to threaten to withhold deliveries of F-35 fighters to Turkey in retaliation for Ankara's purchase of a batch of Russian-made S-400 anti-air missiles.

But with several more shipments of the anti-aircraft missiles due by the end of the summer, Turkish leader Recep Tayyip Erdogan isn't backing down. Rather, during remarks in the capital on Monday, he celebrated the arrival of the missiles, and said he would like to co-produce weapons with Russia, according to RT.

Speaking on the third anniversary of the failed coup attempt that set off one of the greatest purges in Turkish history, Erdogan promised that the newly-acquired S-400 weapons systems would be fully deployed in less than a year. Russian cargo planes began delivering the components on Friday, and more parts are expected to be delivered soon.

The purchase of the S-400 systems has elicited threats of retaliation from the US, which has vowed to cut Turkey, a fellow NATO member, off from sales of advanced weapons like the F-35, while also threatening sanctions (last year, Trump terminated a preferential trade agreement with Turkey in the spat over the S-400).

If Turkey continues to cooperate with Russia on things like arms purchases, expect Washington to impose sanctions and tariffs as Turkey tests the future of NATO.