Eleven women were among those arrested by counter-terrorism officers at four addresses in the Bornova and Buca districts of Izmir, the official said on condition of anonymity due to restrictions on speaking to the media.
They are thought to have lived with the attacker -- who remains at large -- in the central Anatolian city of Konya, the official added.
Earlier, Foreign Minister Mevlut Cavusoglu revealed authorities had identified the attacker who killed 39 people when he stormed the Reina nightclub in Istanbul’s Ortakoy district in the early hours of Jan. 1. They have also released security camera images of the suspect.
The police official said night vision equipment, a sniper scope, an ammunition belt and other military equipment were found during the raids. Twenty children found at the addresses have been taken into temporary care.
On Monday and Tuesday, 16 people were arrested on suspicion of links to the attack.