The dawn raids across the country came just a week after Erdogan narrowly won public blessing for the controversial changes to the constitution to create a presidential system.
They are the latest indication Turkey intends no let-up in the fight against its perceived enemies after the referendum, with fighter jets yesterday pounding Kurdish militant targets in Iraq and northern Syria.
A total of 1,009 suspects have so far been detained in raids in 72 provinces across the country, the official Anadolu news agency quoted Interior Minister Suleyman Soylu as saying.
Some 8,500 police officers were involved in the nationwide operation, Anadolu reported, adding that arrest warrants had been issued for 390 suspects in Istanbul alone.
Indicating that the numbers detained were set to rise, Soylu said the raids were continuing.
"It is an important step for the Turkish Republic," he added.
The 'Yes' camp won 51.41 per cent of the vote in the April 16 referendum but opponents claim the result would have been reversed in a fair poll.
Turkey accuses the Hizmet (Service) movement Gulen leads of being a "terror organisation" although the group insists it is a peaceful organisation promoting moderate Islam.
The government has repeatedly asked the United States to extradite Gulen, who has been living in exile there since 1999.
Some 47,000 people have already been arrested in Turkey under a nine-month state of emergency in place since the coup bid, a crackdown whose magnitude has raised alarm in the West.
The Turkish parliament just ahead of the referendum extended the state of emergency by another three months to July 19.
It said the simultaneous raids across the country were carried out in cooperation between police and the National Intelligence Organisation (MIT).
The suspects are so-called "secret imams" of Gulen suspected of infiltrating themselves into the police or other state institutions, it reported.
Erdogan has repeated said he will wipe out the "virus" of Gulen from state institutions after the failed coup.
The vast operation targeted big cities like Istanbul as well as Izmir in western Turkey and Konya in the Anatolian heartland.
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