The army sent armed helicopters, reconnaissance jets and a commando unit to the Agri region in southeastern Turkey where clashes were continuing, the Turkish military said in a statement on its website.

Angrily denouncing the violence, President Recep Tayyip Erdogan accused the PKK of seeking "to dynamite the peace in our country and undermine the peace process."

"I strongly condemn this attack. The clashes are continuing. Twenty-five terrorists are currently fighting our troops," Erdogan said in a televised speech in the western city of Sakarya on the Black Sea.

The army said troops had been despatched to the district of Diaydin in Agri after receiving intelligence of a planned "festival" to promote the "separatist terror organisation".

This is official shorthand for the PKK whose actual name is never used by the authorities.

PKK militants opened fire on the Turkish military and the army responded, the army said.

"But in the initial fire four of our soldiers were wounded in different places.

"Reconnaissance aircraft, armed helicopters and a commando unit have been dispatched to the area.

"The clashes are continuing," the army added.

- 'Sad and worrying' -

The unrest marks a rare spike in violence as the government seeks to make peace with the PKK after a decades-long conflict that has cost tens of thousands of lives.

Selahattin Demirtas, the leader of the pro-Kurdish People's Democratic Party (HDP) that acts as an intermediary between the government and PKK, called the clashes "a sad and worrying development".

"A detailed investigation is needed to find out exactly what happened," he said in televised comments.

The government's pointman on the peace process, Deputy Prime Minister Yalcin Akdogan, said he strongly condemned the "terrorist attacks".

"The will of the people cannot be put at stake for a mix of political pressure and violence. Opening fire will backfire on itself," he wrote on Twitter.

The PKK's jailed leader Abdullah Ocalan this year called on militants to take steps to lay down their arms in what many see as a historic breakthrough in the peace process.

The PKK initially fought for independence for Turkey's Kurds but later softened its demands to seek greater rights and autonomy.

The head of the PKK's paramilitary forces Cemil Bayik, who is based in northern Iraq, told German media last week that the PKK did not want to fight Turkey anymore.

He also made an apology to Germans for violent protests the PKK organised in Germany in the 1990s.

However there have been signs the peace process has been stumbling in recent months as Turkey's political forces prepare for legislative elections on June 7.

In a tight battle, the HDP is seeking to win over 10 percent of the vote to qualify for direct representation in parliament.

Should it succeed, this could wreck the plans of the ruling Justice and Development Party (AKP) to win a constitutional majority to change the basic law and create a presidential system under Erdogan.