By Daren Butler and Seda Sezer
ISTANBUL (Reuters) - A battle between Turkish Prime Minister Tayyip Erdogan and Islamic cleric Fethullah Gulen intensified on Thursday, with police arrests, a government move against an Islamic lender and a reported purge of the domestic intelligence agency.
Erdogan accused supporters of U.S.-based Gulen of a "vile betrayal" of Turkey, as he campaigned for a presidential election on Sunday which opinion polls forecast he will win.
"There are threats, blackmail, plots, money extorted from businessmen," he said in a speech to a businessmen, calling for their support in fighting Gulen's movement, which he accuses of seeking to overthrow him.
"Yesterday they stabbed us in the back. Tomorrow they will stab their current colleagues in the back if they get the chance," he said. "I call on those who are still silent in the face of this vile betrayal to reconsider their positions."
Gulen's supporters in the judiciary and police are believed to have played a key role in helping Erdogan neuter rivals in the then dominant military and secular establishment through a series of high-profile court cases.
But Erdogan's alliance with Hizmet (Service) crumbled due to disagreements on policy and government moves to rein in Gulen's movement. The rupture became public in December, when a corruption probe targeting Erdogan and his inner circle became public, leading to the resignation of three cabinet ministers.
As Erdogan spoke, a judge in Istanbul remanded in custody four police officers who were among 32 detained on Tuesday in a widening investigation of wiretapping that has allegedly targeting Erdogan, defense lawyer Omer Turanli said on Twitter.
Nearly 150 officers have been held since July in a probe aimed at what Erdogan calls a "parallel structure" within the police, judiciary and other institutions loyal to Gulen.
Erdogan accuses Gulen of being behind a plot to oust him and has vowed to "go into their lairs" and carry out a "witch hunt" to catch those involved.
Gulen, whose followers say they number in the millions, denies using his worldwide Islamic movement to scheme against Erdogan from self-imposed exile in the United States.
PURGES, BANK PRESSURED
Thursday's arrests follow a wave of purges of the police, judiciary and other state institutions this year which government critics condemn as a symptom of Erdogan's tightening grip on power.
The Vatan newspaper said some 50 members of the MIT national intelligence agency were demoted and put under investigation in Ankara in an operation targeting the "parallel structure". Members of an MIT commission coordinating intelligence by different state agencies were transferred back to the police force, accused of being Hizmet members.
In a speech which focused heavily on his battle against Gulen, Erdogan also stressed what he said was the business dimension of Hizmet.
"They tried to redesign not just politics, the police and judiciary, but the business world as well," he said, alluding to a range of companies allegedly run by Gulen sympathizers.
They include Islamic lender Bank Asya, which has come under pressure to sell assets after major investors withdrew deposits amid hostile government comment about the bank.
State-owned companies and institutional depositors loyal to Erdogan have withdrawn 4 billion lira ($1.8 billion), some 20 percent of the bank's total deposits, according to media reports.
Pressure on the bank intensified on Thursday when the tax office said it had canceled an accord allowing it to collect taxes for the finance ministry.
Its shares were suspended in Istanbul following the news, having tumbled 5.3 percent on conflicting statements from top officials over state plans to buy the bank.
(Writing by Daren Butler and Seda Sezer; Editing by Jon Boyle)