ANKARA (Reuters) - Kurdish militants will attack Turkey's dam construction sites in the mainly Kurdish southeast, the group said in a statement late on Saturday, another blow to a fragile peace process meant to end a three-decade insurgency.

The Union of Kurdistan Communities (KCK), the Kurdish militants' umbrella political group, on Saturday issued a statement saying that Turkey's construction of military outposts, dams and roads for military purposes had violated the ceasefire.

"The Turkish state took advantage of the ceasefire conditions not for a democratic political resolution but to gain an advantageous position in preparation of war by building dozens of guard posts, roads for military purposes and dams in order for a cultural genocide," the statement said.

The Kurdistan Workers Party (PKK) launched a separatist armed struggle in 1984 before moderating its goal to improving the rights of Turkey's roughly 12 million Kurds.

President Tayyip Erdogan, who has boosted Kurdish cultural rights during more than a decade in power, began peace talks with Ocalan in 2012, risking nationalist wrath.

"The Kurdish movement has decided to not to accept this treatment any more, and to mobilize all means necessary, including the guerrilla forces, to stop the construction of all dams," it said.

In a June general election, the pro-Kurdish Peoples' Democratic Party (HDP) passed a 10 percent election threshold for the first time and gained 80 seats in Turkey's 550-seat parliament.

However, Erdogan's ruling AK Party, running a single party government for 13 years, failed to get a simple majority. He mandated Prime Minister Ahmet Davutoglu to form a government last week.

Coalition talks will start on Monday. A possible coalition with the right-wing Nationalist Movement Party (MHP) would be likely to scupper a peace process with Turkey's Kurdish minority, something Erdogan sees as part of his legacy.

(Writing by Ece Toksabay; Editing by Ruth Pitchford)