Turkish officers have detained two foreigners at Istanbul airport over the attack on a nightclub on New Year's Eve, according to AFP.
A manhunt has been underwear since a gunman killed at least 39 people and injured 70 more in an attack on the Reina nightclub. There were an estimated 600 revellers in the club at the time.
Eight suspects were arrested in Turkey in the wake of the atrocity, which was claimed by Islamic State.
There have been reports in Turkish media that the authorities are aware of the one of the suspects' identity. Pictures of him have been released, but he has not yet been named.
Turkish media have reported the police are investigating whether he belongs to the same Isis cell which was behind the attack on Ataturk Airport last year.
More on this as it develops