Istanbul (AFP) - Masked gunmen on Saturday shot dead three Turkish soldiers in the restive Kurdish-majority southeast of the country, the army said, blaming separatist "terrorists" for an attack that threatens to undermine a fragile peace process.

The three soldiers were shot dead while off duty and walking on the street in the town of Yuksekova in Hakkari province of Turkey's extreme southeast bordering Iraq and Iran.

The attackers escaped but a security operation was underway to apprehend them, the official Anatolia agency said.

Reports said that the victims had been shot in the head, from behind, while walking in the centre of the town to collect electrical equipment from a police station.

There was no claim of responsibility for the attack.

But in a statement the army blamed "three terrorists from the separatist terrorist organisation", in a clear reference to the outlawed Kurdistan Workers Party (PKK), which the military never mentions by name.

Some 40,000 people are estimated to have been killed in the three-decade-long insurgency waged by the outlawed PKK for Kurdish self-rule and greater rights in Turkey's southeast.

The PKK has largely observed a ceasefire since March 2013 as the ruling Justice and Development Party (AKP) seeks to thrash out a historic peace agreement with the rebels.

But there has been an upsurge in tensions in recent weeks over the government's cautious policy on helping the mainly Kurdish Syrian border town of Kobane, which has been besieged by jihadists of the Islamic State.

- 'No concessions to terror' -

Prime Minister Ahmet Davutoglu blamed the attack on those who wanted to use the Kobane situation to "plunge Turkey into chaos and turmoil".

"These days are a test for everyone," the official Anatolia news agency quoted him as saying in the central city of Kayseri.

"We will take whatever measures are necessary to ensure our national unity and peace in our country," he added.

But he insisted the government's drive to make peace in the southeast would continue, saying the "peace process is not a process that will make concessions to terrorism."

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Tensions have been building for several days. Late on Thursday night, the security forces shot dead three suspected PKK militants after they launched an attack on a power station in the Kagizman district of the eastern Kars region, Anatolia reported.

The armed wing of the PKK, the HPG, confirmed in a statement Saturday that three of its "guerrillas" had been killed in the clash.

The Turkish army also sealed off the eastern city of Tunceli on Saturday following reports that a cemetery for slain PKK fighters was to be opened there.

Earlier this month, Turkish jets bombed Kurdish rebel targets in the southeast of the country for the first time since the ceasefire, in response to attacks on a military post.

Over 30 people were killed in deadly pro-Kurdish protests in Turkish cities this month against the government's stance on the Kobane standoff.

However the jailed leader of the PKK, Abdullah Ocalan, said in a statement this week that he remained hopeful that the peace process would be concluded successfully.

But Davutoglu condemned the PKK as a threat not just for Turkey but the whole region and said the government's main interlocutor in the peace talks was not "the terror organisation" but the people.

Ankara has been wary of backing the Kurdish fighters battling the jihadists for Kobane, fearing this will strengthen the PKK.

Turkey's main pro-Kurdish Party, the People's Democratic Party (HDP), said in a statement that the killings were a matter of "great sorrow and concern" and said the peace must process to continue.