Turkey signs Russian missile deal, pivoting from NATO

The deal cements a recent rapprochement with Russia, despite differences over the war in Syria, and comes as Turkey's ties with the United States and European Union have become strained.

It is certain to stir unease in Washington and Brussels, where officials are trying to keep Turkey, a longtime NATO member, and an increasingly unlikely candidate for European Union membership — from entering Russia's sphere of influence. The deal comes as relations between Russia and the West are at a particularly low point. Tensions escalated in 2014 when Russia annexed Crimea and then began fomenting armed revolt in eastern Ukraine. They have grown still worse as evidence has mounted that Moscow was behind the hacking of the 2016 election in the United States and also tried to interfere in other nations' elections.

Although a prospective missile purchase from Russia was made public several months ago, Erdogan's announcement was the first confirmation that Turkey had transferred money to pay for the missile system, known as the S-400.

"Signatures have been made for the purchase of S-400s from Russia," Mr. Erdogan said in comments published in several newspapers on Tuesday. "A deposit has also been paid as far as I know." The purchase of the missile system flies in the face of cooperation within the NATO alliance, which Turkey has belonged to since the early 1950s.

NATO does not ban purchases of military hardware from manufacturers outside the American-led alliance, but it does discourage members from buying equipment not compatible with that used by other members.