Federal police made two arrests and confiscated weapons and marijuana Sunday in Tijuana, across the U.S. border from San Diego, after coming under attack by men linked to a drug cartel.
Police said one of the arrested suspects told them they worked for "the engineer," an apparent reference to a leader of the Arellano Felix drug cartel.
Officers, who were not injured in the attack, seized three assault rifles, pistols and bundles of marijuana.
Mexico is experiencing a wave of violence tied to drug gangs, especially in border states and other areas known as hotbeds of narcotrafficking. The government says more than 1,000 people were killed during the first eight weeks of the year.
On Saturday, two police officers in the town of Praxedis Guerrero were shot dead in their patrol vehicle, prosecutors said.
The town is just south of Ciudad Juarez, a city bordering Texas where more Mexican troops are being sent to fight the cartels.
In the southern state of Guerrero, the governmental National Human Rights Commission issued a report Sunday criticizing state officials for failing to fully investigate the killing of a magazine journalist in 2003.
In the five years since "La Razon" editor Rafael Villafuerte was killed, no suspects have been arrested, the commission said. Villafuerte wrote about government corruption and worked in a part of the country where drug trafficking is rampant.