Two people were killed Saturday in a suicide bombing on Istiklal boulevard, a main high street in the centre of Istanbul, just off Taksim Square.
Seven people were wounded in the explosion near a shopping area, CNN Turk reported.
Emergency services were rushed to the area and ambulances were ferrying people to hospital. The street was largely closed down by police.
The blast 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.
In January, 12 tourists were killed by a suicide bomber in Istanbul in an attack the authorities blamed on Islamic State.
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.