ANKARA (Reuters) - Turkey has not changed its decision to buy S-400 missile defense systems from Russia but welcomes a U.S. State Department approval of the possible purchase of a rival Patriot system from the United States, two Turkish officials said on Wednesday.

One official described the State Department decision as good signal for Ankara’s troubled relations with Washington, and Turkey was now waiting for the next U.S. step.

“Turkey has not changed the decision to buy the S-400 defense system from Russia,” the official said. “As an ally, the U.S. should sell it to Turkey...but we have been waiting their approval.”