Local authorities made the discovery early on Tuesday morning on a route that links the broadly peaceful states of Puebla and Tlaxcala.
Police have not given a motive for the killings or said which of the criminal groups operating in Mexico might have carried them out.
Local media has reported that a blanket was left at the scene with a message issuing a warning to rival gangs and apparently signed by a group called "La Barredora", meaning "the sweeper".