The weekend clashes in several cities, which left two protesters dead and saw four Turkish soldiers briefly kidnapped, were the worst since Kurdish rebels announced a ceasefire nine months ago.

Prime Minister Recep Tayyip Erdogan on Sunday accused certain groups of trying to damage the peace process.

"These are actions perpetrated by those who want to hurt the process," Erdogan said. "However, we will continue the process... without falling into this trap."

The wave of unrest was triggered by reports that cemeteries containing the bodies of fighters from the outlawed Kurdistan Workers' Party (PKK) in the southeastern town of Yuksekova had been destroyed -- claims denied by the local authorities.

Two protesters were shot dead by police in clashes in Yuksekova on Friday night, setting off weekend protests in several towns including the main southeastern city of Diyarbakir and even Turkey's biggest metropolis Istanbul.

In a statement from his prison cell, jailed PKK leader Abdullah Ocalan denounced the deaths.

"These killings are a great provocation against the peace process," said Ocalan.

Four Turkish soldiers in plain clothes were kidnapped on Sunday in a rural area near Diyarbakir by Kurdish rebels who torched their vehicle and whisked them off to an unknown location.

They were freed on Monday after intervention by lawmakers from the pro-Kurdish Peace and Democracy Party (BDP), a local security source said.

"The soldiers were returned to the local authorities and are in good health," the source told AFP.

In the past, Kurdish rebels frequently kidnapped soldiers, workers and local officials as bargaining chips for the release of captured PKK members.

In Diyarbakir on Sunday, police fired tear gas and water cannon to break up a demonstration by around 5,000 people brandishing effigies of Ocalan.

Protesters also hurled explosive devices at a police station in the town of Dogubeyazit near the Iranian border and set fire to a local bank branch in Hakkari near the frontier with Iraq.

Around a dozen people, including four policemen, were injured in Diyarbakir alone, and around at least 22 protesters were arrested, local media reported.

The latest incidents come after months of calm between the Turkish state and the PKK, which declared a truce in March following clandestine negotiations between Ocalan and the country's spy agency.

The process stalled after Kurdish rebels announced in September they were suspending their retreat from Turkish soil, accusing the government of failing to deliver on promised reforms.

The violence erupted after Erdogan's government on Thursday submitted to parliament a so-called "democratisation" package of reforms mainly affecting Kurds.

The reforms include education in Kurdish in private schools, election campaigns in Kurdish and the removal of a ban on the use of the letters Q, W and X, which are used in Kurdish spelling but not in Turkish.

Kurds are also demanding the release of Kurdish prisoners and political activists, the lifting of restrictions on Kurdish-language education in state schools and reducing the 10-percent election threshold required to secure seats in parliament.

The PKK, which is blacklisted as a terrorist organisation by Turkey and much of the international community, launched an insurgency seeking self-rule in the southeast in 1984 that has claimed about 45,000 lives.