Two assailants, believed to be members of the rebel Kurdistan Workers' Party (PKK), opened cross-fire with rifles on the van while it was driving through the center of the city of Batman, the sources said, adding that a security operation was under way to hunt them down.

Two policemen sustained serious injuries and died shortly after in hospital.

In a separate incident earlier Monday, a passer-by was injured when a time bomb exploded under the car of an army officer, parked outside his home in the town of Idil, near the borders with Iraq and Syria.

The authorities suspect the blast was the work of the PKK, which has often carried out similar attacks in the past as part of a bloody separatist campaign in the southeast.

At the weekend, a radical Kurdish group which the authorities say is a cover-up for the PKK, claimed responsibility for a bomb attack targeting a police building in the western city of Izmir, which left one person injured.

The Kurdish conflict in Turkey has claimed 37,000 lives since 1984 when the PKK, blacklisted a terrorist group by Turkey as well as the European Union and the United States, took up arms for Kurdish self-rule in the southeast.

Unrest in the region has significantly escalated since June 2004 when the PKK called off a five-year unilateral ceasefire with the government.