"This act of betrayal translates not only the desperation but also the loss of reference points of the terrorist organisation," Erdogan told reporters in the main Kurdish city of Diyarbakir, referring to the separatist Kurdistan Workers' Party (PKK).

No one has claimed responsibility for Thursday's attack, which killed five people and wounded 68, but Turkish officials blame the PKK.

"Those killed in this attack, weren't they fellow Kurdish citizens? Weren't they people from the region?" Erdogan asked during a visit to central Diyarbakir where the blast occurred.

During his visit, Edogan also met with soldiers wounded in the blast as well as relatives of the victims.

Four of the dead were high school students attending classes at a nearby private school. The wounded included about 30 soldiers.

The PKK, which has waged a bloody 23-year campaign for Kurdish self-rule in southeast Turkey, had threatened to retaliate against Turkish air strikes on its bases in neighbouring northern Iraq last month.

Investigators believe the bomb was made of about 40 kilogrammes (88 pounds) of explosives of a type the PKK has frequently used, a police source said earlier this week on condition of anonymity.

Diyarbakir was the target of a 2006 explosion that killed 10 people and was also blamed on the PKK.