The United States has yet to respond to a proposal to set up a technical committee to review possible security threats that Russia’s S-400 missile defense system could pose to the U.S. F-35 fighter jet program, stated Turkish Foreign Minister Mevlüt Çavuşoğlu, AP reported.

Speaking at a news conference with his Polish and Romanian counterparts Friday, Mevlut Cavusoglu said Turkey is taking utmost care to ensure that the S-400 system is under full Turkish control. He added that Turkey does not believe that the S-400 would threaten the F-35 program, of which Turkey is also a partner.

Turkey’s decision to acquire Russia’s S-400 missile defense system aggravated the situation between Washington and Ankara. US officials warned of the consequences until the imposition of sanctions. Turkish officials say the deal cannot be canceled.