Five people were killed Saturday in a suicide bombing on Istiklal boulevard, a main high street in the centre of Istanbul, just off Taksim Square.
The five fatalities include the bomber.
At least 20 people were wounded in the explosion near a shopping area, said Vasip Sahin, the governor of Istanbul, Turkey's largest city and economic hub.
Emergency services were rushed to the area and ambulances were ferrying people to hospital. The street was largely closed down by police following the attack just before 11 am (0900 GMT).
The street is usually bustling at its busiest times in the evening, although the morning hours on the weekend often see less shoppers.
The blast, near a fish market, comes as Turkey is on edge, following a massive car bombing in Ankara on March 13 which killed 37 people.
That attack was claimed by the Kurdistan Freedom Falcons (TAK), a splinter group of the banned Kurdistan Workers' Party (PKK).
A similar attack last month in the capital left 30 dead and was also claimed by TAK.
The attack in Ankara this month was preceded by a warning from the US embassy about a potential terrorist act in the area.
German diplomatic missions and schools were closed this week in Istanbul and Ankara following what was described as a "concrete" terrorism threat, apparently from Islamic State.
However, after two days of being shut, authorities said the embassy in Ankara and consulate in Istanbul would reopen on Monday.
In January, 12 tourists were killed by a suicide bomber in Istanbul in an attack the authorities blamed on Islamic State.
The combined effect of the attacks as well as the war in neighbouring Syria and a diplomatic row with Russia is having a devastating impact on Turkey's vital tourism sector.
Violence has been spiralling in Turkey since last summer. The largest terrorist attack in the country's history came in October, when 100 people were killed in an attack in Ankara blamed on Islamic State.
Meanwhile, the country has seen the conflict with militants from the Kurdish minority reignited after a two-year ceasefire collapsed in July and peace talks were abandoned.
Hundreds have died, including civilians, in the mostly Kurdish south-eastern regions of the country in recent months.