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