CULIACAN, Mexico — Mexican authorities say at least 12 state police officers and a bystander have been killed in an ambush on a highway in Mexico's western state of Sinaloa.

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Sinaloa state security officials say the attack happened around 6 p.m. Friday at a fake checkpoint set up by gunmen on the highway near the town of Guasave.

The police convoy was traveling from Los Mochis, a Pacific coastal city where the officers helped launch a "Safe Commerce" program aimed at averting attacks on merchants.

Officials say the slain bystander was driving from a nearby tortilla stand where he works and got caught in the crossfire.

An attack on police earlier in the day in Los Mochis wounded two police officers.