ANKARA (AFP) - Turkey's parliament Wednesday extended the government's mandate to order strikes against Kurdish rebels in northern Iraq as an attack on a police bus in the country's southeast, killed four people. The assault came just days after rebels from the Kurdistan Workers' Party (PKK) killed 17 soldiers in a daytime attack on a military outpost near the border with Iraq. Of the 529 lawmakers present in the 550-seat chamber, 511 backed the motion giving the government another year-long mandate for cross-border operations against PKK hideouts in northern Iraq. Only 18 lawmakers voted against the motion. As parliament was in session, suspected PKK assailants opened fire on a bus carrying employes of the police academy in Diyarbakir, the main city in the Kurdish-populated southeast, killing the driver and three police officers. Fifteen other police officers were injured in the attack, the local governor's office said. The bloodshed is likely to increase nationwide outrage triggered by Friday's attack which saw PKK rebels try to take out an outpost in the border province of Hakkari, under cover of heavy weapons fire from northern Iraq. The ensuing clashes killed twenty-three militants, the army said. Security operations intensified inside Turkey after the assault and four militants were killed in Sirnak province late Tuesday, while a wounded soldier died in hospital in Diyarbakir, officials said Wednesday. Speaking ahead of the parliamentary vote, Prime Minister Recep Tayyip Erdogan stressed Turkey's right to self-defence and said Ankara would launch a cross-border incursion if necessary to rout the rebels. Such an operation will be carried out "if need be, at the right time and under the right conditions with a view of obtaining the right result," Erdogan said Tuesday.