A small bus carrying eight foreign tourists flipped over while traveling over Bolivia's famous salt flats, killing the driver and three of the passengers, police said Monday.

The accident happened on Sunday at the Salar de Uyuni, the world's largest salt flats. It was the second deadly event involving a vehicle there in two months. On May 2, 10 Japanese and Israeli tourists were killed when two Sport Utility Vehicles collided and burst into flames. The driver of one of the vehicles and a Bolivian tour guide also died.

In Sunday's incident, the driver braked suddenly, causing the van to spin around three times and then flip over, said area police commander Julio Cepcel.

Police are investigating several theories, including that the driver was speeding or that he came upon a sudden hole or other obstacle on the flats.

The victims were identified as Marie Soutif, 58, and Marcelle Gilberte, 48, both of France; and Ben J. Bollon, of Belgium, 28. Police did not release the victims' hometowns. The Bolivian driver's identity was not released.

Four other tourists, two from Belgium, one from Japan and one from Germany, were taken to a local hospital with unidentified injuries, Cepcel said.

The cloud-white flats are located in Bolivia's southwest corner, 280 miles (450 kilometers) south of La Paz, and are one of Bolivia's main tourist attractions. They span 4,085 square miles (10,580 sq. kilometers) and penetrate as far as 30 feet (9 meters) deep.