Turkish authorities arrested more than 1,000 people on Wednesday they said had secretly infiltrated police forces across the country on behalf of a U.S.-based cleric blamed by the government for a failed coup attempt 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 President Tayyip Erdogan who is now accused by the government of trying to topple him by force.