Gul described Friday's attack by the Kurdistan Workers' Party (PKK) as "treacherous" and said Ankara was determined to crush the militants.

"The struggle against terrorism is a long-term, not a short-term, process... Let me underline once again that we will continue the struggle (against the PKK), whatever the cost," Gul said in a video message posted on his office's website.

"We are investigating how this treacherous attack took place, who facilitated it. These will be followed up on and everyone will be held to account," he added.

The president's remarks appeared to be a veiled warning to Iraqi Kurds whom Ankara accuses of failing to curb PKK rebels using the mountainous north of Iraq as a springboard for attacks on Turkish targets.

In the bloodiest attack this year, PKK rebels, backed by heavy weapons' fire from bases in northern Iraq, launched an assault on a military post near border Friday, killing 15 Turkish soldiers.

Twenty-three PKK rebels were killed in the ensuing fighting which lasted late into Friday night, an army spokesman said.

A separate statement from Gul's office said that in light of the attack, the president cancelled a one-day visit to France on Monday during which he was to deliver a speech at a conference organized by the French Institute of International Relations (IFRI).