Police took 33 of their colleagues into custody on Tuesday in Istanbul, Ankara and across southeast Turkey, NTV said, days ahead of the country's first presidential election which opinion polls forecast Erdogan will win.
More than 100 officers were detained in July in the same investigation, aimed at what Erdogan calls a "parallel structure" within the police, judiciary and other institutions loyal to U.S.-based Islamic cleric Fethullah Gulen.
Erdogan accuses Gulen, a former ally, 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, Reuters reported.
"The structure in the parallel police has started to emerge," Erdogan said in an interview with Kanal 24 late on Monday, accusing Turkey's main opposition parties of operating in tandem with Gulen.
"God willing this will come to an end. But I have to say that we are just at the beginning of this business," he said, describing Gulen's movement as a threat to national security. "The judiciary has now started to do what is necessary."
Gulen and his Hizmet, or 'Service', movement denies scheming against Erdogan, but the alliance between Hizmet and the government has crumbled in recent years.
Of the 115 officers detained in July, 31 have been remanded in custody pending possible trial. Many of them have said the case against them was politically motivated.
The arrests follow a stream of purges targeting the police, judiciary and other state institutions this year which government critics have condemned as a symptom of Erdogan's tightening grip on power.
Gulen, whose followers say they number in the millions, is believed to have built up influence in the police and judiciary over decades and leads a powerful worldwide Islamic movement from his self-imposed exile in the United States.