The outlawed Kurdistan Workers' Party (PKK), which has waged a bloody 26-year separatist campaign in southeast Turkey, was expected to announce later Monday its decision on whether to end or extend a truce it declared in August.

Interior Minister Besir Atalay said investigators had obtained clues on Sunday's attack at Taksim square, in the heart of Istanbul, but stressed that more time was needed to make a definite conclusion.

"We have findings... We have information... But we will make a statement once we are sure and after various dimensions (of the attack) have been evaluated," Atalay told reporters.

No one has been detained so far in connection with the incident, he said.

The bomber blew himself up at a police patrol at Taksim Square, Istanbul's busiest spot popular also with foreign tourists, as he tried to get into a police bus, wounding 17 civilians and 15 police officers. No one was in life-threatening condition.

The evidence obtained so far has led security forces to focus on the PKK as the most likely culprit, the popular Milliyet edaily reported Monday.

The suicide bomber used A4 explosives, a type that several PKK militants were caught carrying recently in operations across the country, it said.

A senior security official, quoted by the liberal Radikal daily, said the evidence was leading investigators to rule out the other major suspect -- militants of underground far-left groups, which have also targeted the police in the past.

"The actual suspicion has focused on the obvious organisation or some of its elements who are out of control or have split up from the group," the unnamed official said, referring to the PKK.

The attack coincided with the expiration of a unilateral ceasefire that the PKK had announced on August 13.

Top PKK commander Murat Karayilan last week said the group would no longer target civilians and wanted to extend the truce indefinitely if the government demonstrated a commitment to dialogue for a peaceful solution to the Kurdish conflict.

The PKK, listed as a terrorist group by Turkey and much of the international community, took up arms for self-rule in the Kurdish-majority southeast in 1984, sparking a conflict that has claimed around 45,000 lives.