ISTANBUL — A bomb rocked a major pedestrian thoroughfare in the heart of Istanbul on Sunday, killing six people, injuring several dozen and sending people fleeing the blast.

Emergency vehicles responded to the scene on Istiklal Avenue, a popular thoroughfare lined with shops and restaurants that leads to the iconic Taksim Square. In video posted online, a loud bang was heard and a flash was seen as pedestrians turned and fled.

Turkish President Recep Tayyip Erdogan called the blast a “treacherous attack” and said its perpetrators would be punished.

He did not say who was behind the attack, but said it had a “smell of terror” without offering details, adding that he still wasn’t sure. The president said police and the governor’s office were conducting investigations, including reviewing footage of the area.

Erdogan said that six people were killed. Vice President Fuat Oktay later updated the number of injured to 81, with two in serious condition, also saying it appeared to be a terrorist attack.

Numerous foreign governments offered their condolences, including neighboring Greece, with which relations are strained. Prime Minister Kyriakos Mitsotakis said he was “shocked and saddened by the news of the heinous attack.”

Turkey was hit by a series of bombings between 2015 and 2017 that left more than 500 civilians and security personnel dead. Some of the attacks were carried out by the Islamic State group, while others were carried out by Kurdish militants who led a decades-long insurgency against the Turkish state for greater autonomy or independence.

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Turkey has been fighting the militants, known as the PKK and considered a terrorist organization by Turkey, the United States and the European Union, in the country’s southeast for years.

Following the series of attacks, Turkey launched cross-border military operations in Syria and northern Iraq against Kurdish militants, while also cracking down on Kurdish politicians, journalists and activists in the country through sweeping anti-terrorism laws that critics say , are a way of silencing dissent.

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

Access to some content on Twitter and other social networking sites, such as videos, was limited.

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