"I was naive. I used my best endeavours to support him," Erdogan told party loyalists at an election rally, referring to Gulen, who lives in exile in the United States.
Erdogan has blamed Gulen and his supporters in Turkey of launching a major corruption probe targeting key members of his inner circle that has shaken his government to the core ahead of key elections on March 30.
At the rally in the southwestern city of Isparta, Erdogan accused Gulen of interfering in Turkish politics and urged him to return to the country.
The Gulen movement was a key backer of Erdogan's Islamic-rooted Justice and Development Party (AKP) when it first came to power in 2002.
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The two came together to tame the influence of Turkey's once-powerful military which staged three coups since 1960 as the self-declared guardians of the secular state.
But the alliance shattered after December police raids which saw which dozens of Erdogan's key business and political allies detained on allegations of bribery in construction projects, gold smuggling and illicit trade with Iran.
In the latest episode in the escalating feud, the Turkish parliament passed a bill Friday to shut down thousands of private schools many of which are run by the Gulen movement.
The legislation sets September 1, 2015 as the deadline to close down the schools, which were one of the sources of the row between the Gulen movement and the AKP.
"They are going to lose USD 1 billion annual income (from the schools). That's why they are going mad," said Erdogan.