A leader of the outlawed Kurdistan Workers Party (PKK) warned on Saturday it had called all its fighters back to Turkey and could resume attacks, after protests over the government's policy on Syria left dozens dead.

Cemil Bayik, one of the founders of the PKK which has waged a bloody 30-year insurgency for Kurdish self-rule in Turkey, said the peace process with Ankara was in danger of collapse after the deadly unrest.

"We have warned Turkey. If the state carries on like this then the guerrillas will resume the war of defence in order to protect the people," Bayik told German broadcaster ARD in an interview recorded in Iraq.

As part of a fragile peace process, the PKK had started withdrawing its fighters from Turkey and moving them to its military base in northern Iraq.

But Bayik said these fighters had now returned to Turkey in reaction to the policies of the ruling Justice and Development Party (AKP).

"Because Turkey has continued its policies without changes, we have sent back all the fighters who were withdrawn," he said.

He did not reveal how many fighters had left the base at Mount Kandil in northern Iraq to return to Turkey. The size of the PKK's total fighting force is estimated at around 5,000.

Kurds are furious that Turkey has not intervened to defend the mainly Kurdish Syrian border town of Kobane from Islamic State (IS) jihadists.

Moreover, Turkey has actively prevented Kurds from crossing into Syria to join the fight against IS because it fears it would lead to the creation of an effective Kurdish fighting force at its border.

The anger boiled over into violent protests across Turkey last week that according to official figures left 31 dead and 360 wounded.

"The AKP is responsible for what is going on in Kobane and Turkey," Bayik told ARD.

- 'Declaration of war' -

The PKK's overall leader Abdullah Ocalan, who is serving a life sentence in an island prison on the sea of Marmara, has given the government until mid-October to come up with a roadmap to save the peace process.

But President Recep Tayyip Erdogan vowed Saturday to do everything possible to save the peace process, denouncing those who he said wanted to sabotage the search for a deal.

"Everyone must know that the acts of violence, vandalism and pillaging that we saw in the last days have nothing to do with Kobane," Erdogan said in a televised speech in the Black Sea town of Rize.

The Turkish government earlier this month obtained authorisation from parliament for military action in Iraq and Syria but Bayik claimed this was aimed more against the PKK than IS.

"The IS terror militia is barely mentioned in this authorisation (for military action)." he said. "But the PKK is very much mentioned.

"With the passing (of the authorisation) in parliament, Turkey ended the peace process and it amounts to a declaration of war," he said.

However, Bayik's rhetoric is considerably sharper than that of Ocalan, whom Kurds regard as having the final word on the peace process.

New demonstrations took place overnight in Turkey's largest Kurdish city of Diyarbakir but protests appear to have calmed somewhat, for now, after four days of bloody violence.

The world's largest stateless people, Kurds are spread between Iran, Iraq, Syria and Turkey and make up around 15-20 percent of the Turkish population.

The PKK has fought the Turkish authorities since 1984 in a rebellion that has claimed 40,000 lives. It has largely observed a ceasefire since March last year but peace talks are currently frozen.