By Gulsen Solaker and Humeyra Pamuk
ANKARA (Reuters) - Turkey's Prime Minister Tayyip Erdogan on Wednesday denounced a corruption crackdown on his allies months ahead of elections as a "dirty operation" to smear his administration and undermine the country's progress.
He said those behind the investigation were trying to form a "state within a state", an apparent reference to the movement of U.S.-based Turkish cleric Fethullah Gulen, whose followers are influential in Turkey's police and judiciary.
A total of 52 people, including three ministers' sons, prominent businessmen close to Erdogan and local government officials, were detained on Tuesday in the country's biggest corruption probe since Erdogan swept to power in 2002.
"As we fight to make Turkey in the top 10 countries of the world ... some are engaged in an effort to halt our fast growth. There are those abroad ... and there are extensions of them within our country," Erdogan told a news conference.
"Right now a very dirty operation is going on."
Several dozen senior police officers, including the heads of the financial crime, organized crime and smuggling units in Istanbul and at least 18 others in Ankara, were removed from their posts following the detentions, local media said.
Edrogan said officers had been removed for abuse of office and warned more could follow in other cities.
Tensions have grown in recent months between Erdogan's government and Gulen's Hizmet (Service) movement over plans to close private schools which prepare teens for competitive high school and university entrance exams, some run by Hizmet.
The schools, part of a global education network, are an important source of revenue and influence for Gulen's movement, creating a web of contacts and personal loyalties among a religious-minded elite in Turkey and abroad.
A lawyer for Gulen denied he had any hand in the probe.
"The honorable Gulen has nothing to do with and has no information about the investigations or the public officials running them," Orhan Erdemli said in a statement published by Turkish media outlets.
Erdogan drew parallels with weeks of violent anti-government protests over the summer, which grew out of a demonstration against plans to redevelop Istanbul's Gezi Park. Riot police clashed night after night with demonstrators protesting against what they said was Erdogan's growing authoritarianism.
"There is a process that started with the Gezi incidents. They could not get what they wanted there and now they have taken a new step," Erdogan said.
Representatives of Hizmet have always denied being behind June's protests but tacitly chided Erdogan, who dismissed the protesters as "riff-raff", throwing their weight instead behind more conciliatory voices in his AK Party.
HEART OF RULING PARTY
Erdogan and Gulen both draw support from religiously minded, conservative Turks in the mostly Muslim country of 75 million people, but there have long been ideological differences which have bubbled increasingly to the surface.
Many of Gulen's followers see him as a more progressive and pro-Western influence than Erdogan, whose opinions on issues from abortion to alcohol consumption, and the concentration of power around him they view with increasing alarm.
Gulen could not challenge Erdogan at the polls and has shown no intention of forming a party, but their battle for influence could shape the Turkish political landscape for years to come.
"This does mark a battle for the heart and mind of the party, and for the likely policy orientation," said Timothy Ash, head of emerging markets research at Standard Bank.
The Hizmet movement has helped Erdogan's Islamist-rooted AK Party win a growing share of the vote in three successive elections over the past decade, but the rift between the two sides risks fracturing their common support base.
Gulen runs the network of schools and other social facilities across the Middle East, Asia and Africa from a compound in the United States. He moved to the United States in 1999 after being charged with attempting to undermine the secular state.
He was later acquitted but has remained in Pennsylvania, an enigmatic figure who gives little hint of his intentions in Turkish politics, viewed with suspicion by secularists who see him seeking to infiltrate state and cultural institutions.
BATTLE LINES DRAWN
The Istanbul prosecutor's office, which has been leading the corruption investigations, has showed no sign of backing down.
In its first official comment since Tuesday's detentions, it said it was conducting three separate inquiries, two of which dated back to September 2012, and that two additional prosecutors had been appointed to assist.
In a brief statement about the removal of senior officers, the police said some staff had been reassigned, in some cases due to alleged misconduct and others "out of administrative necessity", but gave no further details.
The corruption investigation dominated newspaper headlines.
Pro-government papers accused Gulen's followers of running a smear campaign against the AK Party before municipal elections in March and a presidential race a few months later in which Erdogan is expected to run.
"The black propaganda escalates," the daily Star newspaper said on its front page. "Somebody has pushed the button on the eve of the municipality elections."
Deputy Prime Minister Bulent Arinc also said the corruption probe was part of an effort to tarnish the government but played down any suggestion he meant Gulen's followers were behind it.
"It is incorrect to associate a meaning to my comments that would create a confrontation with the community," Arinc told a news conference, referring to Gulen's movement, whose adherents say they number in the millions.
(Additional reporting by Ece Toksabay and Ayla Jean Yackley in Istanbul; Writing by Nick Tattersall; Editing by Alison Williams)