The sources said a fourth soldier had died of his wounds following clashes on Saturday with Kurdistan Workers Party (PKK) militants in the province of Hakkari, southeast of Tunceli near the borders with Iran and Iraq.
The PKK, deemed a terrorist organisation by the United States and the EU, has been fighting an insurgency since 1984, demanding greater Kurdish autonomy in the southeast of the country. Some 40,000 people have been killed in the fighting.
The conflict has surged again since a two-year ceasefire collapsed in July, leaving peace negotiations in tatters, weeks ahead of a general election on Nov. 1.
The violence persists despite a PKK call a week ago ordering its forces to halt all actions in Turkey unless attacked.
The government has dismissed the move as an election gambit to bolster the pro-Kurdish opposition ahead of the parliamentary election and has said military operations will continue until PKK fighters disarm and leave Turkey.