A bomb exploded on a popular pedestrian street in Istanbul on Sunday, killing six people, wounding dozens and sending people fleeing as flames rose.

Footage posted online showed ambulances, fire trucks and police at the scene on on Istiklal Avenue, a typically crowded thoroughfare popular with tourists and locals and lined with shops and restaurants. In one video, a loud bang could be heard and flames could be seen, as pedestrians turned and ran away. Social media users said shops were shuttered and the avenue closed down.

Turkish President Recep Tayyip Erdogan called the blast a “treacherous attack” and said its perpetrators would be punished. In addition to the six dead, Erdogan said another 53 were wounded, according to information he received from the Istanbul governor.

Turkey was hit by a string of deadly bombings between 2015 and 2017 by the Islamic State group and outlawed Kurdish groups.

Five prosecutors were assigned to investigate the blast, state-run Anadolu news agency reported.

Turkey’s media watchdog imposed temporary restrictions on reporting on the explosion — a move that bans the use of close-up videos and photos of the blast and its aftermath. The Supreme Council of Radio and Television has imposed similar bans in the past, following attacks and accidents.

(AP)