Turkish authorities said they had arrested more than a thousand “secret Imams” who had infiltrated police forces on behalf of a U.S.-based cleric accused by President Tayyip Erdogan of trying to topple him last July.

The nationwide sweep was one of the largest operations in months against suspected supporters of the cleric, Fethullah Gulen, a former ally of Erdogan. Gulen denies any part in the coup led by military officers.

Interior Minister Suleyman Soylu said the overnight crackdown targeted a Gulen network “that infiltrated our police force, called ‘secret imams’.

“One thousand and nine secret imams have been detained so far in 72 provinces, and the operation is ongoing,” he told reporters in Ankara.

Another 9,103 personnel from Turkey’s police force were suspended on Wednesday, police headquarters in Ankara said in a statement on its web site, citing alleged links with Gulen’s network.

In the aftermath of the failed July coup, authorities arrested 40,000 people and sacked or suspended 120,000 from a wide range of professions including soldiers, police, teachers and public servants, over alleged links with terrorist groups.

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