Turkish police on Saturday detained 28 people over links to President Recep Tayyip Erdogan's archfoe, US-based cleric Fethullah Gulen, Dogan news agency reported.
In the latest crackdown, police carried out simultaneous raids in several cities including Istanbul as well as Konya and Kayseri in central Anatolia, the agency said.
Among other charges, the suspects are accused of "membership in a terrorist organisation," the Hurriyet newspaper reported on its website.
Police are searching for 23 other people including Rizanur Meral, the head of major business group the Turkish Confederation of Businessmen and Industrialists (Tuskon), according to Dogan.
Founded in 2005, Tuskon has 55,000 members and supporters of Erdogan accuse it of financing pro-Gulen activities.
Ankara accuses Gulen of plotting to overthrow the Turkish government and running a "terror" group.
But his supporters have repeatedly denied the charges.
The latest arrests came months after some 100 Gulen supporters were detained in similar raids in April.