At least nine people were killed and four injured in an unexplained explosion Thursday in an indigenous area in Colombia’s mountainous southwest, local authorities said, Reuters reported.

The incident came on the tenth day of a blockade of the area’s major highway. Hundreds of members of indigenous groups have halted traffic on the roadway, demanding land titles and funding for social programs.

One policeman has been killed during the protest. Several vehicles have also been burned.

The explosion took place in a house in Dagua municipality, an area largely inhabited by indigenous groups.

Colombia, which has more than 45 million inhabitants, has more than 85 ethnic groups. About a million Colombians are members of indigenous groups.