The bodies of six kidnap victims have been recovered from a house in Mexico, following a three-hour shootout between gunmen and soldiers and police.
Mexican soldiers and police battled the heavily-armed drugs gang
The men had been killed by a shot to the head, a federal agent told a news briefing in the border city of Tijuana.
The stand-off began as agents prepared to raid a house that police say was a hideout for the Tijuana drugs cartel, also known as Arellano Felix.
It is the latest in a series of drug-related killings in Mexico.
Tijuana is the biggest city in Baja California, which was Mexico's most violent state in 2007 with more than 400 murders.
President Felipe Calderon sent more than 3,000 soldiers to Tijuana earlier this month, as part of a nationwide crackdown on drug trafficking and gang violence.
During the incident nearby schools were closed down, and local television showed images of police officers carrying out children while gunfire was heard in the background.
A spokesman for the federal Public Safety Department, Edgar Millan, said one of the gunmen had been killed and four police officers wounded.
Another four gunmen were arrested - one of whom was a state police investigator and another a Tijuana police officer, said Mr Millan.
The four men will be flown to Mexico City for questioning.
Investigators are trying to determine the identities of the six men found shot dead in the house.