In one of their bloodiest assaults this year, the Kurdistan Workers' Party (PKK) militants targeted a military unit near the Iraqi border overnight with rocket launchers and assault rifles, killing six soldiers, military sources said.

The Turkish army said in a statement that nine soldiers had been lightly wounded in the attack on the unit near the border town of Cukurca, while Prime Minister Recep Tayyip Erdogan put the figure at 15.

"The region has been reinforced with helicopter gunships and troops. Operations are underway," the arm's statement said.

The PKK claimed that the attack, which started at 2:00 a.m. (2300 GMT), had killed 13 soldiers and said there were no casualties among rebel ranks.

PKK's foreign relations chief Roz Walat, based in Iraq where the rebels have rear bases, added that his fighters had also destroyed Turkish mortars and canons before fleeing.

In a separate attack, PKK rebels fired on a group of soldiers on a security sweep near Gurpinar in the eastern province of Van Tuesday, killing one of them, local military sources said.

In Ankara, Erdogan said his government was determined to crush the rebels.

"We will pursue our struggle with determination. We will continue fearlessly and tirelessly. We will not take even one small step back," he said.

The PKK dramatically stepped up its 26-year separatist campaign after its jailed leader Abdullah Ocalan said through his lawyers in late May he was abandoning efforts to seek dialogue with Ankara.

The flaring unrest dealt a severe blow on an already fragile government initiative, announced last year, to expand Kurdish freedoms and boost investment in the Kurdish-majority southeast in a bid to erode separatist sentiment in the region and cajole the rebels into laying down arms.

The government rejects dialogue with the PKK, listed as a terrorist group by Ankara and much of the international community, dismissing criticism by Kurdish activists that any peace effort is doomed to fail unless the PKK is included.

A declaration signed by 649 non-governmental organizations from 20 provinces across the country called for end to violence by both sides and the launch of a dialogue with the rebels for peace.

"The Turkish Armed Forces should cease their operations and the PKK must end their attacks," read the declaration issued Tuesday.

"A process of dialogue must be launched to enable a lasting solution and no party to this conflict should be excluded from this process," it added.

Ankara has in recent years granted Kurds a series of cultural freedoms, but has failed to draw up a clear strategy on how rebels could be persuaded to abandon violence and reintegrated into society.

The PKK has threatened to spread violence to urban centres in western Turkey.

Last month, radical Kurdish militants claimed responsibility for a remote-control roadside bomb that hit a bus carrying army personel in Istanbul, killing five soldiers and the teenage daughter of an officer.

Under pressure for tougher measures against the rebels, Erdogan said last week Ankara was planning to deploy specially-trained professional soldiers along the Iraqi border to fight the rebels and stop them infiltrating Turkish soil.

Since 2007, the Turkish army has often bombed PKK hideouts in northern Iraq and carried out a number of cross-border ground operations to pursue the rebels.

The PKK took up arms for Kurdish self-rule in the southeast in 1984, sparking a conflict that has claimed some 45,000 lives.