"The incident is still being evaluated and the cause of the explosion will become clear after bomb experts complete their investigation," a spokesman for the Istanbul police told AFP.
He declined to comment on press reports that Saturday's blast outside a cafe was caused by a bomb believed to have been set off by a timer or remote control.
A Dutch tourist and a waiter were injured in the blast that occurred under one of the tables outside a cafe under the Galata bridge over the Golden Horn on the European side of the city.
Istanbul police chief Cellalettin Cerrah told reporters on Saturday the explosion had not been set off by a gas leak, but he would not elaborate on what could have caused the blast.
Istanbul, a sprawling metropolis of about 12 million people, has in the past been the target of bomb attacks by underground left-wing organisations and Muslim militants.
The PKK has denied any role in
Kurdish rebels, leading an armed campaign against the government, have also been blamed for a number of bomb attacks in the city.
The outlawed Kurdistan Workers Party (PKK), which took up arms in 1984 for Kurdish self-rule in Turkey's southeast, has intensified its attacks on the army over the past several months, after it called off a five-year unilateral ceasefire in June 2004.
Police believe the PKK was behind a 16 July bomb attack in the seaside resort town of Kusadasi in the west of the country that killed five people, including a British and an Irish tourist, and injured 13 others.
The PKK, considered a terrorist organisation by the United States and the European Union, denied any involvement in the bombing.
The Kusadasi bombing came a week after a bomb explosion in the nearby resort of Cesme that injured 20 people.
The Kurdistan Freedom Falcons (TAK), a little known group Turkish officials say is linked to the PKK, claimed responsibility for the Cesme bombings, threatening more attacks on tourist targets.