Turkish prosecutors have issued an arrest warrant for Fethullah Gulen, an influential cleric and head of the eponymous movement who is in self-imposed exile in Pennsylvania, US, according to state broadcasting channel TRT Haber.
Gulen and his movement, also called Hizmet (service), have been accused of orchestrating a wave of high-profile arrests that shook the moderate-Islamist government of the then-prime minister and current president Recep Tayyip Erdogan. Forty-seven businessmen and politicians, including the sons of three Cabinet ministers, were put in custody on corruption and bribery charges.
The 70-year-old preacher, who is accused of "leading a terrorist organisation", denied any involvement.
Erdogan accused Gulen of orchestrating the scandal against his inner circle in an attempted "judicial coup" and of building a "parallel state" with extensive influence in the Turkish police and judiciary. Reports that Gulen members infiltrated the secret services, law enforcement offices and the AK party itself have circled in Turkish media for some time.
If confirmed, the move would be Erdogan's boldest step against the former ally.
Meanwhile, an Istanbul court has released the editor-in-chief of Turkey's largest daily newspaper, Ekram Dumanli of Zaman. His arrest was part of a police operation against Gulen-linked media that included the arrest of 23 people, accused of forming an illegal armed terrorist organisation and trying to seize control of the state.
Their arrests came just two days after Erdogan vowed to "overthrow" what he called a "network of treason" with clear reference to Hizmet.
Tensions between Gulen and Erdogan, a former ally, worsened over the past few years and exploded with the graft probe in December.
The former prime minister and current president sought to purge the judiciary and police of Gulen's influence and called for the cleric's extradition to Turkey.
The row extended to businesses linked to the preacher, in particular to Islamic lender Bank Asya, which saw its shares drop after state-owned firms and institutions withdrew huge deposits earlier this year.
Both Gulenists and Erdogan's AK party were long persecuted by the secularist generals that saw themselves as guardians of the secular state founded by Mustafa Kemal Ataturk, the father of modern Turkey.
When the moderate Islamist AKP took power in 2002, the Gulen movement provided indispensable support for Erdogan with its extensive influence in the media, police and judicial system.
After AKP swept to a second term five years later, pro-Gulen prosecutors cracked down on generals through the "Ergenekon trial" of hundreds of alleged coup plotters.
Gulenists seized the opportunity to take revenge on former rivals, including the military.
World-renowned journalists such as Ahmet Sik and Nedim Senerwere searched and arrested in 2011 for their work critical of Gulen's network.
But the struggle for power and influence in Turkey turned the former friends against each other for the control of Turkish politics.