"President Recep Tayyip Erdogan's narrow win in the mid-April popular referendum on expanding his powers and the ruling Justice and Development Party's (AKP's) post-coup crackdowns are increasing societal and political tension in Turkey," Coats stated in written testimony.
Additionally, he noted Turkey's relations with the United States have been strained due in part to the inclusion of the Syrian Kurdish People's Protection Units (YPG) in the US-led coalition against the Islamic State terror group (banned in Russia).
Turkey considers the YPG to be a Syrian branch of the Kurdistan Workers Party (PKK), which both Ankara and Washington consider to be a terror group.
Coats added that US-Turkish relations are also under pressure over the issue of extraditing Fethullah Gulen, a Turkish cleric living in the United States who Ankara blames for orchestrating a failed coup last July.
Erdogan is set to visit the United States next week, and Justice Minister Bekir Bozdag met US Attorney General Jeff Sessions on Tuesday to discuss Gulen's activities.
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