A shop was also damaged in the attack, leaving two people injured.

The two other injured were police officers.

Some witnesses said the device hurled at the vehicle was a hand grenade.

It was not immediately known who was behind the attack.

The separatist Kurdistan Workers' Party (PKK), listed as a terrorist group by Ankara and much of the international community, is active in the region and has routinely targeted the security forces.

The attack followed Prime Minister Recep Tayyip Erdogan's announcement earlier in the day that the government was drafting a motion asking parliament to authorise a cross-border military operation into northern Iraq to crack down on PKK militants who take refuge there.

The government decided Tuesday to step up measures against the rebels, "including a cross-border operation if necessary," following an upsurge in PKK violence.

Fifteen soldiers were killed in rebel attacks at the weekend, triggering a huge public uproar and turning up pressure on the government for tougher action.

The PKK has waged a bloody campaign for Kurdish self-rule in the southeast since 1984. The conflict has claimed more than 37,000 lives.