Assailants gunned down at least 13 local police officers in southern Mexico's Guerrero state on Monday, a state government source told Reuters, in the latest brazen attack in a region where gangs have been vying for control over drug trading.
Among the dead is the local security chief for the town of Coyuca de Benitez, the source said, speaking on condition of anonymity.
The town is located to the west of the popular beach resort of Acapulco.
In a statement later on Monday, state officials said security in the area would be reinforced, including by the navy and National Guard agents, but did not say how many police had been killed.
The Coyuca de Benitez area is known for the presence of organised crime.
Prior to the ambush, the agents were sent to respond to a report of alleged firearm detonations in the area, the source said.
Violence has spiked in Guerrero over the past decade as a growing number of criminal gangs battle for control of the lucrative opium poppy trade, as well as for other smuggling routes.
During the first nine months of this year, nearly 1,100 people have been murdered in the state, up by nearly a quarter compared to the previous year, according to official data.