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By Alexandra Hudson and Gulsen Solaker
BERLIN/ANKARA, July 21 (Reuters) - Turkey's peace process with Kurdish militants will go on whether or not Tayyip Erdogan wins the presidency in August, his pro-Kurdish rival said, but he declined to reveal whether he would back the prime minister in the event of a second-round run-off.
Selahattin Demirtas, the presidential candidate for the pro-Kurdish Peoples' Democratic Party (HDP), is running a distant third in the polls. He left unclear which of the leading candidates he might support.
Support from Kurds, who make up a fifth of the population, could be key to Erdogan's securing the absolute majority he needs in the first round of the presidential election on Aug. 10, or equally important in the event of a run-off two weeks later.
Erdogan has done more than any previous Turkish leader to advance Kurdish rights, and he is hoping to benefit from Kurdish support as a result, in the country's first direct election for the presidency.
Under his leadership, Turkey began peace talks with jailed Kurdish militant leader Abdullah Ocalan in 2012, in an effort to end a 30-year-old insurgency that has killed 40,000 people.
But Demirtas said the future of the peace process did not hinge on Erdogan alone.
"The negotiation process is not just a process dependent on Erdogan," he told Reuters in a telephone interview from the western German city of Cologne, where he addressed Turkish citizens over the weekend.
"If I was president, I would make better progress. (The main opposition presidential candidate) Ekmeleddin Ihsanoglu has said he does not oppose dialogue either," he said.
Support for the HDP is below 10 percent in opinion polls, suggesting a significant proportion of Turkey's Kurds might vote for Erdogan, but the party is aiming to broaden its appeal beyond its Kurdish roots.
Sister party of the recently renamed Democratic Regions Party (DBP), which dominates much of the mainly Kurdish southeast, the HDP was formed late last year to contest mayoral elections elsewhere in Turkey, where Kurds are in a minority.
Demirtas, a 41-year-old human rights lawyer, is significantly younger than either Erdogan, 60, or Ihsanoglu, 70, a former head of the Organisation of Islamic Cooperation (OIC) who is running on the ticket of the main secularist opposition Republican People's Party (CHP).
Despite widespread anti-government protests and a corruption scandal during his past term as prime minister, Erdogan still enjoys huge support and is widely expected to win the presidency.
Two polls last month suggested a comfortable victory in the first round on Aug. 10, putting Erdogan on 55-56 percent, a 20-point lead over Ihsanoglu.
If no candidate wins more than 50 percent in the first round, a runoff vote will be held on Aug. 24.
The scale of support for Erdogan has left Turkey's disparate opposition trying to work out what alliances might dent him.
Demirtas declined to give a percentage of the vote the HDP was targeting, or to say whom it might back in a second round. To do so, he said, "would not be in the spirit of a truly free election." (Editing by Daren Butler)