THESSALONIKI (AP) — A smuggling vehicle crammed with asylum-seekers crashed on a northern Greek highway Friday killing six people, including three children, and severely injuring a further four adults.

Police said the jeep was carrying 16 men, women and children when it veered off the road and crashed into rocks near the town of Kavala. There of the survivors were in hospital with severe head injuries, another was being operated on for bone fractures, while the remaining six were more lightly injured.

The driver, who was a member of a migrant-smuggling gang paid to ferry the asylum-seekers west, was among the dead. Authorities said the migrants were Syrian and Iraqi nationals.

Police said the cause of the crash was unclear, but the vehicle was not being pursued by patrol cars at the time of the accident. Authorities were notified by motorists who saw the wrecked jeep by the roadside.

Police said the vehicle had come from the northeastern Evros region, on the border with Turkey, which is a major crossing point for Middle Eastern, Asian and African migrants and refugees seeking a better life in Europe.

Accidents are frequent, as smuggling gangs try to drive asylum-seekers in desperately overcrowded vehicles as quickly as possible to Thessaloniki, sometimes chased by police.