Those injured in the attack in Taksim Square included 15 police officers and 17 civilians, said Istanbul Governor Huseyin Azni Mutlu. The five people in serious condition were all police officers, he said.

The male bomber died at the scene, Mutlu todl reporters. A second device was found on the bomber's body that either failed to detonate or was not used, he said.

The bomber was trying to get into a police car when he set off the explosion. Security cameras caught the event, and officials were looking over the video for more information, Mutlu said.

He condemned the attack as a "crime against humanity." He would not name the bomber or discuss a motive, and said it was too early to provide information on possible ties to organizations while the investigation was under way.

Earlier, Istanbul Police Chief Huseyin Capkin said the suspected bomber tried to board a police bus parked in the square, but the blast occurred before he did.

Taksim Square houses a commercial district and a major transportation network that includes buses, metro systems and taxis. Visitors throng the area, which is typically patrolled by numerous officers.

The suicide bomber struck when the city was marking National Day, which celebrates the declaration of independence for the Turkish republic. The parade was originally scheduled for Friday, but bad weather forced a postponement.