Bogota  - Six bus passengers were shot to death after armed criminals stopped a bus travelling in the south-western province of Narino, officials said Thursday.

The thugs stopped the bus on the road between the provincial capital of Pasto and the Pacific harbour town of Tumaco, police said.

They then boarded the bus and read out names from a list, pulled the people from the bus and shot them. The motive for the attack was not known, but the circumstances indicated that right-wing paramilitary fighters were involved.

William Montezuma, police chief of Nariono, said it appeared that the victims were merchants who wanted to sell their wares at Carnival in Tumaco.

The Pasto-Tumaco stretch of road is infamous for such violent events. It serves as the main smuggling route for export of illegal drugs and import of illegal weapons, via the harbour town.

Colombia's numerous militia often kill merchants for not paying protection money or to intimidate rivals. (dpa)