Mr Erdogan has accused Mr Gulen's Hizmet network, which has built quiet influence in the police and judiciary over decades, of orchestrating a fraud investigation which has grown into one of the biggest challenges of his 11-year leadership.
He has responded by tightening government control of the courts and reassigning thousands of police officers and hundreds of prosecutors and judges, in what his aides say is a drive to cleanse the judiciary of Mr Gulen's influence.
In his first interview in Turkish media since the scandal burst into the open in December, the US-based cleric, whose worldwide network of followers claim to number in the millions, said he was the victim of a campaign of slander.
He added: "What we are seeing today is 10 times worse than what we saw during the military coups. This inflicts extra pain on us. All we can do is remain patient."