Turkish President Recep Tayyip Erdogan has reaffirmed his country’s commitment to an agreement with Moscow to buy Russian S-400 missile defense systems, saying Ankara will not step back from the deal despite US threats of “devastating” consequences.

“There is a certain step that we took, there is an agreement here and we are committed to it,” Erdogan told reporters on Tuesday, adding that it was “out of the question for us to take a step back” from the deal the two countries finalized almost two years ago

Ankara decided in 2017 to purchase the Russian defense system following the failure of protracted efforts to buy air defense systems from the US.

A number of NATO member states have criticized Turkey for its planned purchase of the S-400, arguing the missile batteries are not compatible with those of the military alliance.