Turkish President Recep Tayyip Erdogan said there is no reason for the United States to worry following reports that Turkey is negotiating the purchase of Russian S-400 air defense systems, the Anadolu news agency reported on Tuesday.

“Why would it be worrying? Every country needs to take certain measures for its own security,” the agency quoted Erdogan as saying.

Erdogan stressed it was important for Turkey to choose a partner for co-production of the S-400 Triumph and added that negotiations on the anti-ballistic missile system were mostly complete.

The Turkish president made the comments a day after the U.S. Joint Chiefs of Staff Chairman, General Joseph Dunford, said that Turkey’s purchase of the Russian air defense system “would be a concern, were they to do that, but they have not done that.”