They include two Israelis with dual US nationality, and an Iranian. Another 36 were injured in the blast near a government building.
No-one has admitted carrying out the attack, the latest in recent months.
The Turkish government has blamed Kurdish militants for previous attacks and has retaliated against them.
Saturday's attack on Istiklal Street in Istanbul, Turkey's largest city, occurred at about 11:00 local time (09:00 GMT).
Uwes Shehadeh was some 500m (1,640ft) away when he heard "a horrific and horrible noise".
