Minutes after a bomb exploded in a telephone booth, a second, more powerful, blast went off in a trash bin a few yards away. The second bomb exploded as the first blast had begun to attract a crowd, NTV television reported.
Istanbul provincial Gov. Muammer Guler told reporters the attack was not a suicide bombing, the Times of London said.
"There is no doubt that this is a terror attack," he said. "The blasts occurred in a very busy district and this raised the casualties."
Guler said investigators would examine video from surveillance cameras to try to determine who placed the bombs.
Turkish President Abdullah Gul issued a statement denouncing the attack reiterating Turkey's commitment to what he called the struggle against terrorism, The New York Times reported.
"Nothing can be achieved by terror, violently claiming lives of the innocent," the statement said. "These attacks show the inhumanity and misery of the assailants."