Mexican authorities say a 12-year-old boy shot dead earlier this week was killed far from the site of a clash between security forces and protesters.

A report from the Michoacan state prosecutor's office says the victim and four other people who suffered wounds were inside a restaurant 1,000 feet (300 meters) from the disturbance.

It says all were hit by shrapnel from bullets of an undetermined caliber, though early analysis suggests they were not military-grade. A soldier had a similar wound.

The Thursday statement says that "it can be affirmed that both civilians and security forces were attacked by persons whose identity is being investigated."

Witnesses have said federal forces fired first in the Sunday clash.