A Turkish newspaper said Monday it plans to sue Prime Minister Recep Tayyip Erdogan in a "treason" row that has highlighted political tensions in the country.

The government lodged a criminal complaint against the liberal Taraf newspaper last month after it revealed documents purporting to detail secret plans by the Turkish strongman to eliminate a powerful religious movement.

Kurdish rebels freed on Monday four Turkish soldiers abducted in the southeast of the country in the worst flareup of violence since a fragile ceasefire nine months ago, a local security source said.

Fighters from the Kurdistan Workers' Party (PKK) torched the soldiers' vehicle and seized the men on Sunday in a weekend of sometimes deadly clashes between Kurds and Turkish security forces.

Police and demonstrators clashed in Kurdish-dominated southeastern Turkey on Sunday as tensions mounted following the deaths Friday of two Kurdish protesters.

Police fired tear gas and water cannons to break up a demonstration by around 5,000 protesters brandishing effigies of the jailed Kurdish leader Abdullah Ocalan in the main town of Diyarbakir.

Turkish police on Saturday used tear gas and water cannon to break up a protest on the sidelines of the funeral of two Kurds shot dead during clashes a day earlier, Agence France Presse reported.

Hundreds of protesters set up barricades of burning tires on a road in the Yuksekova district of Kurdish-dominated southeastern Turkey and pelted officers with stones.

Turkish police on Saturday used tear gas and water cannon to break up a protest on the sidelines of the funeral of two Kurds shot dead during clashes a day earlier, an Agence France Presse photographer reported.

Hundreds of protesters set up barricades of burning tires on a road in the Yuksekova district of Kurdish-dominated southeastern Turkey and pelted officers with stones.

Two protesters were killed on Friday in armed clashes with Turkish police that erupted over claims that Kurdish rebel cemeteries had been destroyed, local media reported.

Some 30 masked men in a group of around 150 demonstrators hurled Molotov cocktails and hand grenades at security forces in the Yuksekova district of Kurdish-dominated southeastern Turkey, the Dogan News Agency said.

Turkey's Foreign Minister Ahmet Davutoglu said Friday he is heading to Armenia next week on his first visit since the failure four years ago of efforts to normalize ties.

The two countries remain deeply at odds over the mass killings of Armenians during World War I and the disputed Nagorny Karabakh region.

Turkey has yet to receive any new bids to supply a new missile system to rival a controversial multi-billion dollar offer by a US-blacklisted Chinese company, a government official said Friday.

"We have asked other companies to present revised bids but that has not yet happened," secretary of state for defense industries Murad Bayar said.

Four mineworkers were killed in accidents at two underground coal mines in Turkey on Friday, an industry official said.

In the deadliest incident, three men were killed in a methane gas blast at a privately-owned mine in the Black Sea province of Zonguldak, an official from the Turkish Hard Coal Enterprises (TTK) told Agence France Presse.

The mayor of Istanbul, the target of protester anger during June's mass anti-government street demonstrations, will be running for office again next year, Prime Minister Recep Tayyip Erdogan said Thursday.

Kadir Topbas, a member of Erdogan's ruling Justice and Development Party (AKP), has been nominated to stand for a third term in Turkey's municipal elections next March.