Gun battles between rival factions of a Mexican drugs cartel have left at least 15 people dead in the city of Tijuana, near the border with the US.
Police said all the dead were from the Arellano Felix cartel, which has come under pressure from a rival gang.
Two were wearing police uniforms or equipment, but are thought to have been gang members, police say.
Drug-related violence is a serious issue across Mexico. Nearly 200 people have been killed in Tijuana this year.
Investigators believe two of the dead were senior hitmen for the Arellano Felix cartel and were identified by large gold rings on their fingers.
The rings carried the icon of Saint Death, a grim reaper figure that gangsters believe protects them, police said.
Since taking office in late 2006, President Felipe Calderon has sent nearly 30,000 soldiers and federal police to fight the drugs cartels.
But the violence continues between drug gangs fighting to control lucrative trafficking routes.
The Arellano Felix cartel rose to prominence in Tijuana in the 1980s. Much of its activities centre on smuggling Colombian cocaine through Mexico to California.
It paid millions of dollars in bribes to local law enforcement officers and was blamed for increasing violence, including the murder of informants and rival traffickers.
The gang has been weakened by the arrest or killing of many of its top leaders, police say.
It has recently come under pressure from a rival gang from the west coast state of Sinaloa, led by Mexico's most wanted criminal, Joaquin "Shorty" Guzman.
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