Turkey on Tuesday has continued to receive Russian S-400 missile defense system, as tenth plane landed on an airbase in the capital Ankara, Turkey’s Defense Ministry said.

Axar.az reports citing Turkish media that on Twitter, the ministry shared a photo of the Russian plane carrying the air defense hardware at the airbase on the outskirts of Ankara, and said: “The tenth plane landed at the Murted Airbase.”

The delivery of components of the S-400 long range air defense system is ongoing, it added.

Following protracted efforts to purchase an air defense system from the U.S. with no success, Ankara signed a contract in 2017 to purchase the S-400s from Russia.

U.S. officials urged Turkey to buy U.S. Patriot missiles, arguing the Russian system would be incompatible with NATO systems and expose the F-35s to possible Russian subterfuge.

Turkey, however, emphasized the S-400 would not be integrated into NATO systems and would not pose a threat to the alliance. It has urged the formation of a commission to clarify any technical issues, but the U.S. has failed to respond to Turkey’s proposal.

The U.S. threatened sanctions over the purchase, with Turkey responding that any sanctions would be met in kind.