Veracruz state Attorney General Reynaldo Escobar Perez said the bodies were left piled in two trucks and on the ground of an underpass near a shopping mall in the city of Boca del Rio.
Police had identified seven of the victims so far and all had criminal records for murder, drug dealing, kidnapping and extortion and were linked to organised crime, Escobar said. He didn't say to what group the victims belonged to.
The Gulf and Zetas drug cartels have been locked in a bloody war for control in Veracruz state over the last year.
Motorists first began tweeting yesterday that masked gunmen in military uniforms were blocking Manuel Avila Camacho Boulevard in Boca del Rio's downtown and pointing their guns at civilians.
"They don't seem to be soldiers or police," a tweet read. Another said, "Don't go through that area, there is danger."
Escobar said police were reviewing surveillance video recorded in the area.
Local media said that 12 of the victims were women and that some of the dead men had been among prisoners who escaped from three Veracruz prisons on Monday, but Escobar said he couldn't confirm that.
At least 32 inmates got away from the three Veracruz prisons. Police recaptured 14 of them.
Earlier yesterday, the Mexican army announced it had captured a key figure in the cult-like Knights Templar drug cartel that is sowing violence in western Mexico.
