Turkish officials estimate about 2,000 PKK fighters are holed up in the mountains of northern Iraq, where they allegedly enjoy free movement and obtain weapons and explosives for attacks in Turkey.
Ankara has often accused Iraqi Kurds, who run the autonomous region, of tolerating and even aiding the rebels, but Abdullah Gul, the Turkish president, said on Saturday that the government would pursue dialogue with Iraqi Kurds to resolve the problem.
The Turkish parliament on Wednesday extended by one year the government's mandate to order cross-border military operations in northern Iraq against the PKK, which has long enjoyed safe haven in the region.
Just as the legislators voted, a police bus was machinegunned in Diyarbakir, the largest city in the predominately Kurdish southeast, claiming five lives.
The PKK claimed responsibility on Sunday for the attack, saying in a statement on its website that it was a "successful action" by its fighters.
The police have detained nine people in connection with the incident, among them three alleged PKK members believed to have taken part in the attack.
Separately, officials said a probable suicide attack was foiled on Saturday after the police arrested an alleged Kurdish fighter carrying explosives in downtown Istanbul, Turkey's largest city.
The suspect - a woman in her 30s who was faking pregnancy - carried 8.8kg of explosives and detonators.
The PKK, listed as a terrorist group by Ankara and much of the international community, took up arms for Kurdish self-rule in the southeast in 1984, sparking a conflict that has claimed about 44,000 lives.