Turkey buried the victims on Monday.
“Of course we are profoundly sad. A young teacher and her daughter being the victims of such a treacherous attack has upset us deeply,” said Orhan Akkaya, a relative of a mother and her 15-year-old daughter killed in the attack.
The grieving father, Nurettin Ucar, was crying over his daughter’s Turkish flag-wrapped coffin.
There has been no claim of responsibility.
“We believe that the order for the attack was given from Kobane,” Soylu said, referring to a city in Syria near the Turkish border.
PKK-affiliated Kurdish militants control most of northeastern Syria and, in 2015, Kurdish fighters drove Islamic State jihadists out of the city.
The Kurdish-led Syrian Democratic Forces (SDF) also denied any role in the attack.
“Our forces have nothing to do with the Istanbul bombing,” said Mazloum Abdi, the chief commander of the US-allied SDF.
Justice minister Bekir Bozdag told A Haber television that a woman had been sitting on a bench for more than 40 minutes, “then she got up”, leaving a bag.
“One or two minutes later, an explosion occurred,” he said.
On Monday, all the benches had been removed from Istiklal Avenue, where residents laid red carnations at the scene of the blast, some wiping away tears and others speaking of their fear of further attacks in the run-up to elections next June.
“We need more security!” said Idris Cetinkaya, who works at a nearby hotel and who came to pay his respects.
“The police just searched my bag when I got here, but that’s the first time in a year. Millions of people come here, anything could happen at any second!”
Istiklal Avenue was previously targeted during a campaign of nationwide bombings in 2015-16 that were blamed mostly on the Islamic State group and outlawed Kurdish militants, killing nearly 500 people and wounding more than 2,000.
On Sunday, Turkish President Recep Tayyip Erdogan denounced the “vile attack” that had the “smell of terror” shortly before leaving for the G20 summit on the Indonesian resort island of Bali.
Kemal Ozturk, a shopkeeper, is among those who fear another explosion ahead of presidential and legislative elections in seven months’ time.
“In an election period it can happen,” the 42-year-old told AFP. “We live with fear”.
Regularly targeted by Turkish military operations, the PKK has also been at the heart of a tussle between Sweden and Turkey, which has blocked Stockholm’s bid to join NATO since May, accusing it of leniency towards the group.