“The explosion might be a terrorist act. A woman is thought to be involved,” Erdogan said in a televised address, without providing details about how he had come to that conclusion.
Vice President Fuat Oktay later updated the wounded toll to 81, with two people in serious condition, and said it appeared to be a terrorist attack.
Erdoğan said that the blast was a “treacherous attack” and that its perpetrators would be punished. He did not say who was behind the attack, which he said had the “smell of terror” without offering details, and added that that was not certain. Erdoğan said that four people died at the scene and that the two others died in the hospital.
Shortly after the blast, Istanbul Gov. Ali Yerlikaya tweeted that it “occurred in Taksim Istiklal Street,” a crowded thoroughfare lined by shops and restaurants, at about 4:20 p.m. local time (8:20 a.m. ET).
“Our wounded are being treated,” he said. “We wish God’s mercy on those who lost their lives and a speedy recovery to the injured.”
The Turkish Red Crescent said blood was being transferred to nearby hospitals.
Social media users said shops were shuttered and the avenue had been closed down. The area, in the Beyoğlu district of Turkey’s largest city, had been crowded as usual on the weekend with shoppers, tourists and families.
Turkey’s media watchdog, the Radio and Television Supreme Council, banned broadcast coverage of the blast about an hour after it occurred — preventing broadcasters from showing videos of the moment of the blast or its aftermath.
It has imposed similar bans in the past after attacks and accidents.
Numerous foreign governments offered their condolences, including neighboring Greece, with which relations are tense. Prime Minister Kyriakos Mitsotakis said he was “shocked and saddened by the news of the heinous attack.”
Istanbul's mayor, Ekrem İmamoğlu, also offered his “condolences to those who lost their lives in the explosion on Istiklal Avenue” on Twitter.
French President Emmanuel Macron expressed his condolences, saying “we share your pain” on the anniversary of 2015 Paris attacks, adding, “We are with you in the fight against terrorism.”
From 2015 to 2017 Turkey was hit by a string of deadly bombings by the Islamic State group, and it outlawed Kurdish groups.
Aziz Akyavas reported from Istanbul and Mithil Aggarwal from Hong Kong.