Unidentified gunmen shot and killed 13 people in two separate massacres in Colombia, police said Saturday.

Seven people were killed late Friday when armed suspects traveling in two vehicles opened fire on a group of young people standing on a corner in a working class neighborhood of Medellin, the country's second largest city.A police report said the motive for the massacre had not been established. Massacres are common in Medellin, home to one of the country's cocaine rings.

Authorities blame much of the city's violence on rivalry between youth gangs working for the Medellin cartel.

In a second massacre Friday, gunmen killed a town councilman and five peasant leaders traveling in a vehicle near Chaguani, 50 miles northwest of Bogota, police said.

The victims were on their way to a meeting with officials in the nearby town of San Juan de Rioseco to discuss violence in the region, said Gustavo Petro, an assistant to the town's mayor.

Petro said one of the victims was a Chaguani town councilman and regional leader of the April 19 Movement, known as the M19. The former rebel group laid down its arms last March and became a political party.

Petro said it was unclear who killed the victims because leftist guerrillas and right-wing death squads are active in the region.