Kurdish rebels are ready to re-enter Turkey from northern Iraq, the head of the group's political wing has said.
The statement by Cemil Bayik, a founding member of the Kurdistan Workers Party (PKK) at his mountain hideout, threatens to revive an uprising unless the Turkish government resumes its peace process soon.
Accusing Turkey of waging a proxy war against Kurds in Syria by backing rebels fighting them in the north, Bayik told Reuters news agency during an interview on Saturday that the PKK had the right to retaliate.
Syria's civil war has complicated Turkey's efforts to make peace with the Kurdish fighters, but the Turkish government strongly denies backing any rebel faction against Kurds in Syria and has held regular talks with the head of a Syrian Kurdish group close to the PKK.
Bayik, PKK's most senior figure at liberty, spoke at a small, heavily guarded house in the Qandil Mountain range in Iraq's Kurdish north, a badge featuring Abdullah Ocalan, the jailed PKK leader, pinned to a pocket on his guerrilla uniform.
Imprisoned on an island south of Istanbul, Ocalan commands the loyalty f a dedicated cadre of fighters - both men and women - who live in the mountains that straddle the borders between Turkey, Iran and Iraq.
Ocalan began talks with Turkish officials last year to halt a conflict that has left more than 40,000 people dead over the past three decades and earned the PKK a place on a list of "terrorist" organisations as designated by Turkey, the US and the EU.
In March, a ceasefire was called and Ocalan ordered his fighters to retreat from Turkey to Iraq's autonomous Kurdistan region, but the withdrawal was suspended last month as the rebels said Turkey had not held up its side of the bargain.
"The process has come to an end," Bayik said in the interview.
"Either they accept deep and meaningful negotiations with the Kurdish movement, or there will be a civil war in Turkey."
As prerequisites, Turkey must improve the conditions in which Ocalan is being held and deal with him on equal terms, guarantee amendments to the constitution and enlist a third party to oversee any further steps in the process, he said.
"Now we are preparing ourselves to send the withdrawn groups back to North Kurdistan if the government does not accept our conditions," said Bayik, who shares his position with a female fighter.
He said the direction of the process would become clear "in the coming days".
North Kurdistan is the term Kurds use to refer to the area of Turkey they lay claim to as part of a larger homeland that also takes in tracts of Iran, Iraq and Syria, referred to as East, South and West Kurdistan respectively.
The PKK took up arms against Turkey in 1984 with the aim of carving out a separate state in the southeast for the country's Kurds, which make up about 20 percent of the population but have long been denied basic political and cultural rights.
Ocalan has since changed his views on violence and statehood, and now seeks devolution of power to Kurds within each of the four countries where they are divided, with an overarching confederation to unite them across the borders.
Negotiations with the PKK were unthinkable until only a few years ago and Recep Tayyip Erdogan, the Turkish prime minister, has staked considerable political capital in peace efforts, widening cultural and language rights for Kurds at the risk of angering large parts of his grass-roots support base.
The effort to negotiate with Ocalan is seen as Turkey's best chance at ending a conflict that has tarnished its human-rights record, held back its EU candidacy and undermined economic growth.