The Turkish government has blamed Kurdish militants for a blast in Istanbul's main shopping street on Sunday.
Six people were killed and 81 others wounded when an explosion rocked a busy pedestrian street in Istiklal Avenue in central Istanbul.
Police have detained 46 people in connection to the attack, including a Syrian woman who Turkish authorities suspect planted the bomb.
They say the woman was trained by Kurdish militants and entered Türkiye through north-west Syria's Afrin region.
Interior Minister Suleyman Soylu said the order for the attack was given in Kobani, a city in northern Syria where Turkish forces have carried out operations against the Syrian Kurdish militia in recent years.
"According to our findings, the PKK [Kurdistan Workers' Party] terrorist organisation is responsible," Mr Soylu said.
No individual or group has claimed responsibility for the attack.
The PKK, blacklisted as a terrorist group by Türkiye as well as its Western allies, has kept up a deadly insurgency for Kurdish self-rule in south-eastern Türkiye since the 1980s.
Regularly targeted by Turkish military operations, the group is also at the heart of a tussle between Sweden and Türkiye, which has been blocking Stockholm's entry into NATO since May, accusing it of leniency towards the PKK.
Justice Minister Bekir Bozdag said: "A woman had been sitting on one of the benches for more than 40 minutes and then she got up".
"One or two minutes later, an explosion occurred," he told A Haber television.
"There are two possibilities," he said. "There's either a mechanism placed in this bag and it explodes, or someone remotely explodes (it)."
No reports of Australians among casualties
Istiklal Avenue was hit during a campaign of attacks in 2015 and 2016 that targeted Istanbul and other cities, including Ankara.
Those bombings were mostly blamed on the Islamic State group and outlawed Kurdish militants, and killed nearly 500 people and wounded more than 2,000.
Sunday's explosion occurred shortly after 12:00am AEDT in the famous shopping street.
The avenue, in the city's Beyoglu district, had been crowded with shoppers, tourists and families, local media reported.
Helicopters flew over the city centre after the attack. Police established a large security cordon to prevent access to the area for fear of a second explosion.
Images posted on social media showed the explosion was followed by a fire and immediately triggered panic, with people running in all directions.
Several bodies were seen lying on the ground nearby.
"I was 50-55 metres away, suddenly there was the noise of an explosion. I saw three or four people on the ground," witness Cemal Denizci told AFP.
"People were running in panic. The noise was huge. There was black smoke," he said.
The Australian government extended its condolences to Türkiye's government and people following the explosion.
"At this time, the Department of Foreign Affairs and Trade has not received any reports of Australians injured or missing," a spokesperson for the department said.
"The Australian Consulate-General in Istanbul is continuing to make enquiries with local authorities to confirm if any Australians have been affected."
World leaders condemn attack
Istiklal is one of Istanbul's most famous arteries and is entirely pedestrianised for 1.4 kilometres.
Crisscrossed by an old tramway and lined with shops and restaurants, it attracts large crowds at the weekend.
Many stores closed early in the neighbouring district of Galata, while some passers-by, who came running from the site of the explosion, had tears in their eyes.
A massive deployment of security forces barred all entrances and rescue workers and police could be seen.
Türkiye's radio and television watchdog, RTUK, placed a ban on broadcasters showing footage of the blast, a measure previously taken in the aftermath of extremist attacks.
Access to social media was also restricted after the attack.
A reaction came quickly from Greece, which "unequivocally" condemned the blast and expressed condolences to the government and people of Türkiye.
White House Press Secretary Karine Jean-Pierre said: "We stand shoulder-to-shoulder with our NATO ally Türkiye in countering terrorism."
French President Emmanuel Macron said in a message to the Turks: "We share your pain. We stand with you in the fight against terrorism".
"Shaken by news of the despicable bombing in Istanbul targeting innocent civilians," Israeli President Isaac Herzog tweeted in Turkish and English. "The whole world must stand united and firm against terror."
Ukrainian President Volodymyr Zelenskyy also tweeted in Turkish: "The pain of the friendly Turkish people is our pain".
ABC/Wires
