In comments carried by its media mouthpiece, the Kurdistan Workers' Party's (PKK) leadership said it had decided to extend a truce which was first declared on August 13 until the country goes to the polls.

"Our movement... has decided to extend the non-action process until the 2011 general elections in order to impose a democraric solution process (on Ankara) and ensure that the parliamentary elections in Turkey take place in a healthy environment," said the statement carried by the Firat news agency.

Turkey's next general elections have not been formally scheduled yet but Prime Minister Recep Tayyip Erdogan said last month his party had earmarked the first week of June 2011.

Firat also reported the PKK leadership had denied responsibility for the blast in Istanbul's landmark Taksim Square on Sunday which wounded 32 people.

"It is not possible for us to carry out such an action at a time when our movement has decided to extend a truce process ... We are in no way involved in this attack," said the PKK statement.

Interior Minister Besir Atalay said investigators had obtained clues on the bombing, but more time was needed to make a definite conclusion.

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

No one has been detained so far over the incident, he added.

The bomber blew himself up at a police patrol at Taksim Square as he tried to get into a police bus, wounding 15 officers and 17 civilians. No one was in life-threatening condition.

The bomber used A4 explosives, a type that several PKK militants were caught carrying recently in operations across Turkey, the Milliyet daily reported.

A senior security official, quoted by the liberal Radikal daily, said the evidence was leading investigators to rule out far-left groups.

"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.

Some commentators suggested the attack could be the work of PKK hardliners opposed to dialogue and might point at discord among PKK ranks.

Top PKK commander Murat Karayilan last week said the group would no longer target civilians and wanted to extend the truce indefinitely if Ankara showed a commitment to a peaceful solution to the 26-year Kurdish conflict.

Kurdish attacks on civilians are claimed mostly by a shadowy group which the PKK says is beyond its control. Ankara insists the group is a front for PKK attacks on civilians.

Boosted by its victory in a September 12 referendum on constitutional reform, Ankara has launched a cautious initiative aimed at cajoling the PKK into laying down arms.

The authorities appear to have included jailed PKK leader Abdullah Ocalan in the effort, with his lawyers acting as intermediaries and holding meetings with him on the prison island of Imrali.

Even though behind bars since 1999, Ocalan retains influence over the PKK and often issues guidelines to the rebels through his lawyers.

In comments on the suicide bombing Monday, Erdogan decried inadequate European support against terrorist groups, an apparent reference to the PKK.

Such attacks "are the product of terrorist organisations and the countries that tolerate them," he charged, without giving names.

Ankara has long accused European countries of tolerating PKK activities on their soil and failing to ban organisations linked to the rebels.

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.