Turkish official news agency Anadolu reported that the Prime Minister Binali Yildirim's Chief Adviser Birol Erdem was detained on suspicion of connections to US-based cleric Fethullah Gulen.
Gulen is suspected of responsibility for 2016's attempted coup, and his movement is considered a terror group by the Turkish government.
Both Erdem and his wife were taken into custody on Saturday in Ankara, and are under investigation.