Guatemalan prosecutors say they have detained eight army privates and a colonel on allegations they carried out extrajudicial killings by opening fire on a peaceful protest, killing eight people and wounding 34 last week.

The country's attorney general's office says it is the first time troops have been prosecuted for their actions during a protest since the 1996 end of Guatemala's civil war.

Prosecutor Claudia Paz y Paz said Thursday that soldiers ignored police instructions to stay away from the protest by largely Indian demonstrators in western Guatemala over high power rates and constitutional changes. After the demonstrators blocked a highway, some of the soldiers arrived and opened fire. Paz y Paz said investigators found at least 104 shells from ammunition of a type used by the army.