The bomb, which went off opposite a square in Kocaeli where the demonstration was taking place, was designed to make a loud noice rather than kill, the city's police chief Huseyin Namal told the Anatolia news agency.

It was planted among shrubs on a pedestrian refuge.

Five people suffered minor injuries, Namal said, and Anatolia reported that a young girl was among them.

There was no immediate word about the perpetrators.

The demonstration, organised to condemn mounting violence by the separatist Kurdistan Workers' Party (PKK), continued after the incident, Anatolia said.

Turks have taken to the streets since last week when a PKK ambush near the Iraqi border left 12 soldiers dead.

The PKK, listed as a terrorist group by Ankara and much of the international community, has fought for Kurdish self-rule in the east and southeast since 1984. The conflict has claimed more than 37,000 lives.

The PKK as well as Islamist radicals and far-left underground groups have carried out bomb attacks in Turkey in the past.