Ankara (dpa) - An agreement to buy the S-400 air defence system from Russia - a move that has caused concern among NATO allies, especially the United States - was necessary, says Turkish Foreign Minister Mevlut Cavusoglu."We need an air defence system. I needed it urgently. We wanted to buy from our NATO allies, but it did not work out," he said, citing a range of problems. "Russia gave me the best deal. And that is why I bought it from Russia," he added. He conceded that a key Turkish demand, technology transfer, was still not yet concluded with Russia, even as other parts of the deal - reportedly worth 2.5 billion dollars - were set to move ahead, with first deliveries slated for 2020."They told us in principle that there will be joint production and also technology transfer. But this is an issue to negotiate in the medium-term and long-term."dpa shg cy mga ncs