Mexican authorities say they found the bodies of six kidnapping victims after hundreds of police fought a three-hour battle with gunmen in Tijuana.
They say the victims were discovered tied up, gagged and shot execution-style in a house. One member of the Arellano Felix drug cartel was killed in Thursday's battle.
Authorities also arrested four suspects - two of whom are police officers.
Four police officers were injured in the gunbattle, which forced the evacuation of nearby schools. Mexican television showed people running for cover to escape the gunfire.
The violence is the latest in the Mexican government's crackdown on drug cartels.
Earlier this week, drug gangs in Tijuana killed three police officers, as well as the wife and two daughters of a policeman, and a young couple and their three-year-old son.
Mexican President Felipe Calderon has launched a nationwide campaign to crack down on gangs and drug-related violence.
Some information for this report was provided by AP and Reuters.