One SI and constable of Harra police station area of the district along with two others were in the vehicle when the accident took place, police said.
Police officials rushed three critically injured persons to hospital where they were declared brought dead by the doctor, police said.
After the incident, locals have alleged that it was police vehicle and in protest they pelted stones on the other vehicles plying on the road, police said.
The bodies were handed over to the family members after the post-mortem, they said, adding that the probe is on.