At least eight men were reported dead Tuesday in the northern Mexican state of Durango after a gun battle between suspected drug traffickers, authorities said.
The early morning shootout took place on a highway near the town of Vicente Guerrero, about 400 miles northwest of Mexico City.
Officials shed little light on possible motives for the gun battle, the latest in a wave of violent incidents that have erupted around Mexico in recent weeks.
A spokesman for the Durango state attorney general's office said officials discovered fragmentation grenades and high-powered firearms at the scene.
None of the dead bore identification, said the spokesman, Ruben Lopez.
All were dressed in black, he said.
"The initial theory is that it involved a confrontation between organized crime groups that until now we have not been able to identify," Lopez said.
Authorities also found a dozen late-model vehicles that had been reinforced with armor, he said.
Durango, about 300 miles south of the border city of Ciudad Juarez, is not known as a hot spot for drug violence. But it abuts the states of Chihuahua and Sinaloa, both of which have been the scene of violent turf wars between drug traffickers.
Mexican President Felipe Calderon dispatched 2,000 soldiers and federal police to Sinaloa last week amid warring between rival factions of a major drug cartel, violence that has killed more than 200 people this year, according to Mexican media tallies.
One of those factions is believed to have been behind the May 8 assassination in Mexico City of Edgar Millan Gomez, the acting chief of the Federal Preventive Police.
Authorities suspect that Millan Gomez was targeted by Arturo Beltran Leyva, formerly a top aide to drug lord Joaquin "Shorty" Guzman. Beltran Leyva has reportedly broken off and allied his faction with a group known as the Zetas, which has served as the armed wing of the so-called Gulf cartel.
In Chihuahua, the Gulf cartel has been locked in a bloody turf war with the group that has dominated drug trafficking there from its base in Ciudad Juarez.
Also, the Baja California attorney general's office said that a California woman whose body was among four discovered fatally shot on a hillside outside Rosarito Beach on Sunday had a criminal record in Mexico.
Libey Gianna Craig, 28, of La Mesa, a suburb of San Diego, had been arrested several times on drug, weapons and human-smuggling charges, according to Mexican authorities.
The other three victims were Mexican citizens. Two had criminal records in the U.S., authorities said. Police still have not discovered a motive in the case, which is the latest in a string of homicides in the Tijuana area.
Craig, whose purse was found containing her passport and a hypodermic needle, according to authorities, had been reported missing by her father on May 8, authorities said.
More than 1,300 people have been killed nationwide this year, according to media tallies. Most of the slayings have taken place in half a dozen states that are hubs for drug trafficking and organized crime.
Times staff writers Cecilia Sanchez and Richard Marosi contributed to this report.