Turkey's defense minister said he had a "very constructive" talks with US Acting Defense Secretary Patrick Shanahan and their views have got closer on some subjects, state-owned Anadolu news agency reported on Wednesday.Defense Minister Hulusi Akar had been visiting Washington with a large Turkish delegation for talks which have in part focused on areas of discord between the NATO allies, chiefly the purchase of a missile-defense system and the war in Syria."The talk was very constructive and occurred with a very positive approach," Akar said of his meeting with Shanahan, according to Anadolu. "We gladly observed that they understood many subjects much better and have got very close to our views on these subjects."He did not specify which subjects he was referring to.Secretary of State Mike Pompeo said last week Washington had told Ankara it could face retribution for buying Russian S-400 missile defense systems under a sanctions law known as Countering America's Adversaries Through Sanctions Act (CATSAA).President Tayyip Erdogan's spokesman Ibrahim Kalin said on Tuesday Turkey expects President Donald Trump to use a waiver to protect it if the US Congress decides to sanction Ankara over the planned S-400 purchase.Turkey has not backed down from the acquisition and said it should not trigger sanctions as Ankara is not an adversary of Washington and remains committed to the North Atlantic Treaty Organization.US officials have said the S-400 purchase would risk Ankara's partnership in the joint strike fighter F-35 program because it would compromise the jets, made by Lockheed Martin Corp. Turkish companies produce some of the parts for the F-35 stealth fighter jet.Akar said Turkey had fulfilled its responsibilities on the issue of the F-35 project and that the training of Turkish pilots and maintenance teams was continuing."We expect the other eight countries who are partners in this project to fulfill their responsibilities towards us," he said.Ankara has proposed to Washington that the two countries establish a technical committee under the NATO umbrella to determine whether the S-400s endanger the F-35 jets as the Americans argue, and is waiting to hear back from the United States.The United States and other NATO allies that own F-35s fear the S-400 radar will learn how to spot and track the jet, making it less able to evade Russian weapons.The disagreement is the latest in a series of diplomatic disputes between the NATO allies, including Turkish demands that Washington extradite cleric Fethullah Gulen, differences over Middle East policy and the war in Syria, and sanctions on Iran.