Turkish soldiers and Kurdish fighters clashed in the most intense battles of the separatist conflict this year, with 18 people killed in three army outposts in the southeast, Turklsh officials and security sources say.
Up to 100 Kurdistan Workers Party (PKK) fighters launched simultaneous attacks at dawn on Tuesday on the three military observation points in Hakkari province near the mountainous border with Iraq, killing eight soldiers and wounding 16, the sources said.
In subsequent clashes Turkish troops killed 10 PKK fighters, the Hakkari governor's office said.
The attacks came at a time of new efforts in Turkey to address the grievances of the Kurdish minority to end a conflict that has scarred the region for three decades.
"I curse this treacherous attack," President Abdullah Gul said in a statement. "The terrorist group wants to sabotage the atmosphere of trust and stability and is continuing its inhumane bloody attacks."
The head of Turkey's pro-Kurdish Peace and Democracy Party (BDP), whose members are frequently accused of ties to the fighters, made a striking call for the PKK to halt hostilities.
"The PKK should stop all kinds of armed activity. The government should also halt [military] operations. Let them give a political solution a chance," Selahattin Demirtas, BDP chairman, told a meeting of the party's parliamentary group.
"This war must end. The deaths must stop. We can't stand by and watch the youngsters kill each other."
The PKK fighters began the co-ordinated attacks with rocket launchers and rifles on the outposts and operations were continuing against the armed group, the sources said.
The fighters were believed to have crossed the border from northern Iraq.
Several thousand PKK fighters are based in mountain hideouts in northern Iraq, from where they regularly launch attacks on state targets in mainly Kurdish southeast Turkey.
General Necdet Ozel, Turkish armed forces chief, rushed to the region, along with the commanders of the ground forces and paramilitary gendarmerie, Turkish media reported.
The interior minister and a deputy prime minister also headed there.
Government and state officials met to discuss the fighting on Tuesday afternoon in Ankara in the office of Prime Minister Tayyip Erdogan, who was attending the G20 summit in Mexico.
The PKK, designated a terrorist group by Turkey, the US and European Union, launched its separatist insurgency in 1984.
More than 40,000 people have been killed.
In his efforts to resolve the conflict, Erdogan has told parliament that Kurdish language lessons could be offered in schools.
He also suggested he was prepared to hold talks with prominent Kurdish politician Leyla Zana after she said she believed he was capable of ending the Kurdish troubles.
Bulent Arinc, deputy prime minister, raised the possibility at the weekend of jailed PKK leader Abdullah Ocalan being put under house arrest if the fighters were to lay down their weapons.
However other leading government figures, pointing to nationalist sensitivities over such a radical move, dismissed the idea and Erdogan said it was only Arinc's personal view.
Concerns about the PKK struggle have been exacerbated by the conflict in Syria, which also has a Kurdish minority.
PKK fighters have launched sporadic attacks in recent months near the Syrian border in Hatay province, where thousands of Syrians are housed in refugee camps.
One Turkish soldier was killed on Monday night in Hatay in a clash with PKK fighters, the governor's office there said.