He expressed concern about the consequences of Ankara's acquisition of the system, noting that it "could pose a risk to Allied aircraft and lead to US sanctions."
“This is Turkey's decision, but the S-400s are incompatible with NATO's missile defense system.
We call on Turkey to cooperate with allies to find an alternative solution, ”TASS quoted Stoltenberg as saying.
Earlier, the head of the Turkish Foreign Ministry, Mevlut Cavusoglu, said that the S-400 had not yet been put on combat duty in the country.
In August, it became known about the signing of a contract for the supply of the second regiment of S-400 air defense systems to Turkey.