NATO Secretary-General Jens Stoltenberg said the bloc was unable to persuade Turkey to abandon the purchase of Russia's S-400 defence system and replace them with systems made by Western countries.
Speaking at a seminar in Washington yesterday, Stoltenberg said this is an important issue for NATO, there must be a possibility to integrate the S-400 air defence systems with the NATO air and missile defence system, adding that so far, this is not possible.
"We have tried to find alternative solutions, such as the Patriot or the French-Italian SAMP/T system. We did not succeed in that, but we will continue our efforts," he added, noting that Turkey is an important ally and played an important role in defeating Daesh.
"No other member has received more refugees than Turkey," he said.
The deal to supply Turkey with Russian-made S-400 defence systems concluded in 2017 and has sparked criticism from Turkey's NATO allies, especially the US.
The United States demanded that Turkey abandon the deal and went as far as imposing sanctions on Ankara. Turkey rejected the demands.