Police in Istanbul are checking cars and passengers at various checkpoints across the Turkish city amid tightening security on Wednesday.
The checks were being carried out as the manhunt continues for the suspect behind the Reina nightclub attack on New Year's Day.
Authorities have identified the attacker, but have not revealed his name.
On Sunday, the UK Foreign and Commonwealth Office updated their travel advice for British tourists to the country and said: "There is an ongoing police operation in Istanbul as a result of the attack."
They added: "You should exercise vigilance and caution at this time, and follow the advice and instructions of the security authorities."
Bullet marks on tables, punctured cushions and a single high-heeled shoe are left as testaments to the New Year massacre at the Reina club.
At least 39 people were killed when a gunman opened fire on a nightclub where more than 500 revellers were celebrating the New Year.