The warning came as Ocalan's Kurdistan Workers' Party (PKK) claimed responsibility for a deadly attack on a convoy of Turkey's ruling party that fuelled tensions ahead of parliamentary elections on June 12.

"June 15 is the deadline. Either a meaningful negotiation process will begin after June 15 or a great war will start and all hell will break loose," Ocalan said in remarks carried by the pro-PKK Firat news agency.

Serving a life sentence since 1999, Ocalan made the comments to his lawyers, who regularly meet him in prison and relay his statements, Firat said.

Despite a series of EU-inspired reforms broadening their rights, Kurds are frustrated that a government initiative of reconciliation, announced last year, has so far been inconclusive.

Aiming to cajole the PKK into laying down arms, officials have held discreet meetings with Ocalan, who retains influence over the rebels and Kurdish politicians, but no tangible progress has emerged.

Ocalan blamed the impasse on the AKP government, arguing that it had failed to respect an "agreement" to halt military operations against the PKK and judicial onslaughts against Kurdish activists, according to Firat.

Prime Minister Recep Tayyip Erdogan, who enjoys solid popularity in the southeast among less militant Kurds, toughened his tone Thursday, slamming Kurdish politicians for cooperating with "terrorists."

Any gesture on the Kurdish conflict ahead of the polls carry political risks for Erdogan at a time when violent Kurdish demonstrations and Wednesday's attack on an AKP convoy have fanned anger among Turks that Kurds are bent on using violence as an instrument to extract political concessions.

Also Friday, the PKK claimed responsibility for the convoy attack, saying it was "a retaliation to police terror against the (Kurdish) people," in a statement carried by Firat.

The assailants ambushed the convoy on a mountain road near Kastamonu, shortly after Erdogan held an election rally in the northern city.

One policeman was killed and another wounded as their car, escorting the convoy, was hit by a hand grenade and cross-fire.

Erdogan had left Kastamonu by helicopter.

The attack "was aimed at the police... and not at civilians or the prime minister," the statement said.

Police have clamped down on almost daily protests in the southeast, which have seen Kurdish youths hurl petrol bombs at the security forces and public property since last month when the electoral board barred several prominent Kurdish candidates from the elections, but then reversed its decision.

Kurdish anger was fanned also by the killing of seven PKK militants in clashes with the army last week, despite a unilateral truce the rebels had declared in August.

In February, the rebels had threatened to end the truce, while saying they would defend themselves "more effectively" against the security forces.

The mounting tensions prompted a warning by leading Kurdish activists Thursday that they might boycott the polls if military operations against the PKK continued.

The Kurdish political leadership, in unison with the PKK, demands autonomy, an amnesty for the rebels and Kurdish-language education in state schools.

The PKK, listed as a terrorist group by Turkey and much of the international community, took up arms in 1984, sparking a conflict that has claimed some 45,000 lives.