The party, usually known by its Turkish initials, PKK, announced a ceasefire in March. It was called by Abdullah Ocalan, the PKK's imprisoned leader.
But a Turkish military convoy was attacked Friday in the southeastern province of Mardin, Today's Zaman reported, with gunmen believed to be PKK fighters firing at it. Gul said he hopes the attack, the biggest break in the ceasefire so far, was a "sudden and unconscious move."
"If someone takes up arms again, the state has stronger arms. This should be known," the president warned.
Turkish officials say more than 100 rounds were fired at the four-vehicle convoy along with a rocket-propelled grenade that missed its target. The attack stopped once the police and soldiers returned fire.