Prosecutors in northern Mexico’s Sinaloa state are investigating the discovery of 20 male bodies with gunshot wounds – including five that were decapitated – on a bridge over a federal highway.

Four decapitated bodies were found hanging from a bridge in the capital of western Mexico's Sinaloa state on Monday, part of a surge of cartel violence that killed 20 people in less than a day, authorities said.

A van containing 16 of the bodies was plastered with a banner referencing the ongoing wars between rival drug cartels in Sinaloa, authorities said.