Turkish authorities arrested more than 1,000 people on Wednesday, April 26 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, Reuters reports.

The nationwide sweep was one of the largest operations in months against suspected supporters of the cleric, Fethullah Gulen, a former ally of President Recep Tayyip Erdogan who is now accused by the government of trying to topple him by force.

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.

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.

The latest detentions came 10 days after voters narrowly backed plans to expand Erdogan's already wide powers in a referendum which opposition parties and European election observers said was marred by irregularities.

The referendum bitterly divided Turkey. Erdogan's critics fear further drift into authoritarianism, with a leader they see as bent on eroding modern Turkey's democracy and secular foundations.

Erdogan argues that strengthening the presidency will avert instability associated with coalition governments, at a time when Turkey faces multiple challenges including security threats from Islamist and Kurdish militants.