At least six people have been killed in Guatemala after protesters clashed with police over rising energy costs.

"We've determined that the number of people who died rose to six," Ana Julia Solis, a spokeswoman for the national human rights prosecutor's office, said on Friday.

Mauricio Lopez Bonilla, the interior minister, confirmed the death toll, but did not provide information on the circumstances that led to their deaths.

However, he said that among the injured, 13 had knife or machete wounds, and another 13 suffered blows.

President Otto Perez Molina said that the violence began when demonstrators fired at security forces in Totonicapan, 170km west of the capital Guatemala City.

Perez denied that the military was involved in the incident, saying he had information that assailants in a civilian truck opened fire on the protesters.

The clashes occurred on Thursday after thousands of Indian tribes blocked sections of the Pan American Highway in Totonicapan to demonstrate.