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Turkish President Recep Tayyip Erdogan says Turkey's decision to purchase Russian-made S-400 missile defense systems doesn't mean that it is seeking "alternatives" in its relations with the West.

Erdogan spoke Monday during a NATO meeting in Ankara attended by alliance Secretary-General Jens Stoltenberg.

The comments came amid a deepening rift with the United States, which says the Russian missiles pose a threat to the U.S. F-35 fighter jet program of which Turkey is also a partner.

Erdogan said Turkey developing ties with "various countries and regions are not an alternative to each other," adding his objection to "such controversies being fired up over the S-400s."

Stoltenberg told state-run Anadolu Agency before his arrival that it was important that NATO allies purchase equipment that is compatible with each other.