Anti-terrorism police have conducted a series dawn raids across Ankara, detaining 29 people, the source who spoke on condition of anonymity due to restrictions on talking to the media, said.
The raids came after Ankara Public Prosecutor’s Office issued arrest warrants for 46 suspects, the majority of whom were reportedly foreign nationals.
Some of the suspects were believed to be preparing for a terror attack on the New Year's Day celebrations, the source added.
A manhunt was underway to apprehend the other suspects in Ankara.
Separately, 46 suspects -- 43 of them foreign nationals -- were detained in Istanbul, a police source said.
The source, who spoke on condition of anonymity due to restrictions on talking to the media, said that the suspects held in Istanbul were also allegedly plotting an attack during the New Year's Day celebrations.
A large number of organizational documents and digital tools have been seized during the operations in both cities.
More than 300 people have lost their lives in Daesh-claimed attacks in Turkey, where the terror organization has targeted civilians in suicide bombings, and rocket and gun attacks.
Turkish security forces have been involved in a long-running campaign to thwart Daesh attacks.