Guatemalan authorities have arrested a colonel and eight soldiers over the alleged extrajudicial killings of eight Indian demonstrators at a protest last week, an official said Thursday.

Attorney General Claudia Paz y Paz told reporters that the prosecution considers Colonel Juan Chiroy to be "primarily responsible" for the fatalities, as he was in command of the troops at the October 4 demonstration.

Those detained, including two women, were being held in barracks in the country's capital on the order of President Otto Perez.

Clashes between Indians and soldiers erupted after thousands of Indians blocked sections of the Pan American Highway in the department of Totonicapan, 170 kilometers (105 miles) west of the capital, to protest hikes in electricity prices.

Investigators found more than 100 shell casings at the scene -- all of them fired from the type of assault rifles used by the army.