Turkey: The first shipment of the Russian-made S-400 air defense missile system has landed in Ankara, in a move that sets up a potential showdown between Turkey and the United States. The equipment arrived at the Muted Air Base on Friday, according to the Turkish Defense Ministry.

President Recep Tayyip Erdogan of Turkey has been insistent in his determination to purchase the S-400 system; Russia’s most advanced antiaircraft weaponry, despite warnings from the United States. Washington has cautioned that the deal will lead to economic penalties against Turkey, a fellow NATO member, and cancellation of Turkey’s purchase of American F-35 fighter jets.

The United States has warned Turkey it will face economic sanctions if it goes ahead with the purchase of a Russian missile defense system.

The United States has been unyielding in its opposition to Turkey’s acquisition of the S-400. American officials have argued that the missile system is incompatible with NATO equipment, and that having Turkey operating both the Russian weapons and the F-35 could give Russia access to the American jets’ secret stealth technology.

A NATO spokesman said on Friday that while member nations decide for themselves what equipment to buy, “we are concerned about the potential consequences of Turkey’s decision to acquire the S-400 system.”