The suspects were members of the "separatist terrorist organization", the euphemism used by officials to describe the outlawed Kurdistan Workers' Party (PKK), Istanbul police said in a written statement.

They were believed to have planted bombs in front of two supermarkets, an office, a medical clinic and a post office on June 29 and July 15, the statement added.

The bombings had caused no casualties, according to media reports.

The suspects were arrested after a demonstration on Sunday during which they injured three members of the security forces "with sticks, stones and explosives," it added.

The PKK, blacklisted as a terrorist organisation by Turkey and the much of the international community, has been waging an armed campaign since 1984 for self-rule in Turkey's mainly Kurdish southeast.

The conflict has claimed some 45,000 lives.

Although the group's main theatre of operation is the southeast, rebels have in the past carried out bomb attacks in major cities while sympathisers have organised pro-PKK demonstrations.