ANKARA - A bomb blast wrecked a bus carrying police officers on Tuesday in the southern Turkish province of Mersin, injuring 18 people in an attack that security sources blamed on Kurdish militants.Seventeen of those hurt were police officers, Deputy Prime Minister and government spokesman Bekir Bozdag told parliament, branding it a terrorist attack."Turkey's battle against terror will continue under any circumstances in a strong and determined way," Bozdag said.Security sources said militants of the outlawed Kurdistan Workers Party (PKK) were believed to have carried out the attack. They also said that none of those wounded were in a critical condition.No one immediately claimed responsibility for the bombing.Local mayor Burhanettin Kocamaz told broadcaster Haberturk the attack took place on a street where the local governor's office was located and had hit the police vehicle as it passed.Images from NTV showed smoke billowing from the area, in Mersin's Yenisehir district. Ambulances, police and fire trucks were sent to the site of the attack, security sources said.Turkey is battling a three-decade insurgency in its mainly Kurdish southeast. The PKK frequently carries out bomb attacks on security forces in the southeast and elsewhere.The PKK is considered a terrorist organisation by the United States and the European Union as well as by Turkey. More than 40,000 people, most of them Kurds, have died since it first took up arms against the state in 1984.