Despite US sanctions threat, Turkey’s defense minister says its military personnel are receiving training to operate the S-400 missile defense system despite U.S. and NATO objections to Ankara’s decision to purchase the Russian technology.

Hulusi Akar also told a group of reporters late Tuesday that Turkey was “making preparations” and “considering all options” against possible U.S. sanctions on Turkey over the purchase.

Turkey’s S-400 deal with Russia has deepened a rift with the U.S., which says the Russian system is not compatible with NATO systems and could put at risk the U.S. F-35 fighter jet program, of which Turkey is also a partner.

Turkey has repeatedly said that the S-400 agreement is a “done deal” and cannot be canceled but Akar said U.S. officials insist that “no deal is a done deal.”