ANKARA, Turkey — Turkey has completed a deal with Russia for the purchase of a Russian antimissile system, Turkish defense officials announced Friday, despite concerns voiced by some of Turkey’s NATO allies.

The deal, which would make Turkey the first member of NATO to own Russia’s most advanced air-defense system, comes amid strengthening ties between Turkey and Russia and the deterioration of Turkey’s relationship with the United States and other Western countries.

A state-run agency, the Turkish Defense Industries Undersecretariat, said in a statement on Friday that Turkey would buy at least one S-400 surface-to-air missile battery with the option of purchasing a second. The delivery of the first battery was scheduled for the first quarter of 2020, the statement said.

The two countries on Friday also completed a financial agreement for the project, under which part of the cost would be financed through a Russian loan, the Defense Industries agency said, without revealing details of the deal.