Turkish police have detained the sons of three cabinet ministers and several high-profile businessmen in a sweeping probe into alleged bribery and corruption that has sent shockwaves across the country.
Tuesday's dawn raids targeted 37 people in Turkey's largest city Istanbul and the capital Ankara suspected of fraud or bribery in connection with public tenders for construction projects, media reports said.
Istanbul governor Huseyin Avni Mutlu confirmed the operation but declined to comment on the details.
"There is an ongoing operation," he told reporters. "It would not be proper to make a statement while the investigation is under way."
It would not be wrong to see the latest bribery operation... as a new phase in the Gulen-government battle.
Prime Minister Recep Tayyip Erdogan's ruling Justice and Development Party (AKP), which boasts of being pro-business, has pledged to root out corruption, a chronic problem in Turkey particularly in the booming construction industry.
But some political observers speculated that the raids stemmed from simmering tensions between Erdogan's Islamic-rooted government and influential Muslim cleric Fethullah Gulen which have burst out into the open ahead of elections next year.
Those detained include the sons of Interior Minister Muammer Guler, Economy Minister Zafer Caglayan and Environment Minister Erdogan Bayraktar.
The suspects also include well-known businessmen and bureaucrats including the chief executive of Turkish state bank Halkbank Suleyman Aslan and construction tycoon Ali Agaoglu, local media reported.
The suspects are accused of accepting and facilitating bribes for some projects and securing construction permits for protected areas in exchange for money, the Hurriyet newspaper reported.
It said the raids were the result of a year-long surveillance operation.
In a speech after the raids, Erdogan vowed he would not bow to any "threat" or "dirty alliances" aimed at ruffling the feathers of his party, although it was not clear if he was referring to the police action or the dispute with exiled cleric Gulen.
"We will not bow to any threat as long as you stand behind us," he said in the central Anatolian city of Konya, a conservative AKP bastion.
"Turkey is not a banana republic or a third class tribal state... Nobody inside or outside my country can stir up or trap my country."
The feud between Erdogan and Gulen hit the headlines last month after the government floated plans to close down a network of private schools run by Gulen's Hizmet movement.
The row exposed fractures in the religiously conservative power base of Erdogan, who has dominated Turkish politics for 11 years, ahead of a highly-charged election year beginning with local polls in March.
"It would not be wrong to see the latest bribery operation... as a new phase in the Gulen-government battle," political analyst Rusen Cakir wrote on his website.
He said the Gulen movement has adopted an "attack is the best defence" tactic.
Gulen, 72, has been living in exile in the United States since 1999 to escape charges of plotting against the secular state but his movement still wields considerable influence within the status apparatus in Turkey including the police and the judiciary.