(CNN) -- Authorities planned funerals Friday for 13 Turkish soldiers killed in what the NATO secretary general condemned as a "terrorist attack" in a southeastern province.
"Such heinous attacks have no justification," Anders Fogh Rasmussen said in a statement Friday about the violence the day before in the NATO member state.
"I express my heartfelt condolences to the families of those who were killed. NATO allies stand in full solidarity against the scourge of terrorism."
The government blamed the hostilities on the Kurdistan Workers' Party, or PKK, a separatist movement regarded as a terrorist group by Turkey, the United States and other entities.
The soldiers were ambushed on Thursday by the PKK during an operation in the town of Silvan in Diyarbakir province, and fighting ensued, the Turkish military said in a statement.
During the incident, hand grenades exploded, igniting a fire that spread in a thickly forested area, resulting in the deaths, the military said.
Along with the 13 soldier deaths, seven PKK members were killed. Seven more soldiers were hurt, two of them seriously, in the fire.
More than 30,000 people, mostly Kurds, have been killed during fighting between the PKK and the Turkish state since the early 1980s. The southeastern region of the country has a large Kurdish population.
Prime Minister Recep Tayyip Erdogan and other ministers along with chief of the armed forces, Gen. Isik Kosaner, and other military leaders, met Thursday in the capital, Ankara, and announced the establishment of a task force to investigate the incident.
"At a time when rights and freedoms are expanding and growing in our country, while brotherhood and peace is gaining strength, the terrorist organization has shown its heinous goals and his treacherous face once more," President Abdullah Gul said in a statement on his website.
"I want to make this clear, such attacks will not deter our government or our nation from finding solutions to our problems ... We will continue our struggle against terrorism with our determination."
Upon arriving in Istanbul, Secretary of State Hillary Clinton expressed support for Turkey.
"We stand with Turkey in its fight against the PKK, a designated terrorist organization which has claimed tens of thousands of Turkish lives," she said in a statement. "We support Turkey in its fight against terror and we will continue to work with the Government of Turkey to combat terrorism in all its forms."
She added that she was planning to meet with Turkey's leaders this week in Istanbul.
Clinton was planning to attend meetings of the Libya Contact Group in Istanbul on Friday and Saturday, and to meet with Gul and Erdogan.
CNN's Talia Kayali and Hande Atay contributed to this report