Five decomposing human heads were left in a sack outside a school in Acapulco, southern Mexico, as teachers from the region strike in protest against drug gang extortion payments.
The remains were found on Tuesday morning on the street outside a primary school along with messages threatening local officials.
Hundreds of schools in the city are currently closed, as many teachers strike in protest against the authorities' failure to protect them from extortion demands by criminal groups. It is not clear whether the heads are meant as a threat against teachers who do not comply with the demands.
Over the last three months, dozens of teachers have been kidnapped and thousands have become victims of an extortion racket that threatens violence against those who refuse to turn over half of their salary.
Guerrero Attorney General Alberto Lopez Rojas confirmed the appearance of a "narco-banner," a public sign hung by criminal groups, threatening the lives of teachers in the state.
The official asserted that the recent wave of violence results from the fragmentation and reorganization of various criminal organizations in the area, in the wake of government actions against the powerful cartels that have left a power vacuum. As InSight Crime has reported, at least one new criminal group has apparently emerged in Acapulco in recent months.