Ankara - Three police officers and one civilian were killed and 15 police wounded Wednesday when two unknown attackers fired at a police service bus in the south-eastern Turkish city of Diyarbakir, the NTV private television station reported.

The service bus was carrying police officers from a police school in the city when it was attacked at around 5 pm (1400 GMT). The attackers fled the scene and police launched a large-scale search operation.

Turkish media said that the attack was similiar to others carried out by the Kurdish Workers' Party (PKK) and may have been carried out in protest against a debate Wednesday in the Turkish parliament on whether to extend for a year a mandate allowing the Turkish military to launch cross-border operations.

The PKK uses the mountainous terrain in northern Iraq as a base from which to launch attacks inside Turkey.

The extension of the mandate was expected to pass easily later on Wednesday. (dpa)