Wednesday's attack in northern Turkey "was carried out by our guerrillas as a retaliation to police terror against the (Kurdish) people," the outlawed Kurdistan Workers' Party (PKK) said in a statement carried by the Firat news agency.

Turkish officials had already blamed the attack on the PKK, which has waged a bloody 26-year campaign for Kurdish self-rule in southeast Turkey.

The assailants ambushed a convoy of the ruling Islamist-rooted Justice and Development Party (AKP) on a mountain road near the northern city of Kastamonu, shortly after Prime Minister Recep Tayyip Erdogan held a rally there ahead of parliamentary elections on June 12.

One policeman was killed and another wounded as the gunmen hurled a hand grenade and opened fire on their car, which was escorting the convoy.

Erdogan had left Kastamonu by helicopter.

The attack "was aimed at the police... and not at civilians or the prime minister," the PKK statement said, condemning police clampdowns on a series of violent Kurdish demonstrations in the southeast recently.

"This is a message to the AKP to pull out its police from Kurdistan, where they brutalise the people," it said, according to Firat.

The group vowed to "use our right to retaliation against those who attack the people."

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.

In February, the rebels had threatened to end a unilateral truce, declared in August last year, while saying they would defend themselves "more effectively" against military operations.