TIJUANA, MEXICO -- At least nine people have been murdered in the northwestern Mexican cities of Tijuana and Ensenada since the start of the weekend, officials said.

A businessman was gunned down Friday night and five other people were killed Saturday in Tijuana, while three people were murdered in El Rosario, a town south of Ensenada, the Baja California state Attorney General's Office said.

The businessman was killed by unidentified individuals who opened fire as state police officers responded to an anonymous tip at the establishment, but none of the officers were wounded.

A father and son were killed by gunfire from 9 mm weapons in the border city's southeast Sanchez Taboada neighborhood.

Two people - a man and a woman - were gunned down and two others wounded on a boulevard in Tijuana's La Mesa section.

Police investigators found 34 bullet casings at the crime scene.

A fourth shooting occurred at an amusement arcade in Rubi, a neighborhood in southwest Tijuana, where one person was killed.

Police in Ensenada, located some 85 kilometers (about 53 miles) south of Tijuana, said two men and a minor were killed in the town of El Rosario.

The three victims were gunned down by unidentified individuals while eating breakfast at a restaurant.

A total of 630 people have been murdered in Baja California state so far this year, according to tallies published by the press and non-governmental organizations.

Some 2,000 people participated in a march in Tijuana, which is near San Diego, California, on Saturday to protest the kidnappings and violence in Baja California.

The march, which was organized by the Tijuana Medical Council and several grassroots organizations, failed to attract as many politicians, community leaders, business people and Catholic Church leaders as expected.

Mexico has been plagued in recent years by drug-related violence, with powerful cartels battling each other and the security forces, as rival gangs vie for control of lucrative smuggling and distribution routes.

Armed groups linked to Mexico's drug cartels murdered around 2,700 people in 2007, and the death toll this year is already at more than 4,500, according to a tally published by the Mexico City daily El Universal.

The majority of the killings have occurred in the states of Chihuahua, Baja California and Sinaloa.

Experts say that Mexico's most powerful drug trafficking organizations are the Tijuana cartel, which is run by the Arellano Felix brothers, the Gulf cartel and the Sinaloa cartel. Two other large drug trafficking organizations, the Juarez and Milenio cartels, also operate in the country.

The Sinaloa organization is the oldest cartel in Mexico and is led by Joaquin "El Chapo" (Shorty) Guzman, who was arrested in Guatemala in 1993 and pulled off a Hollywood-style jailbreak when he escaped from the Puente Grande maximum-security prison in the western state of Jalisco on Jan. 19, 2001, and has been a major headache for authorities and rival drug lords ever since.

Guzman, considered extremely violent, is one of the most-wanted criminals in Mexico and the United States, where the Drug Enforcement Administration has offered a reward of $5 million for him.

Tackling the problem of drug-related violence, according to experts, is a major challenge both because of Mexico's notoriously corrupt security forces and because honest police officers are fearful of taking on the heavily armed drug mobs.

Since taking office in December 2006, President Felipe Calderon has deployed more than 30,000 soldiers and federal police to nearly a dozen of Mexico's 31 states in a bid to stem the wave of violence unleashed by drug traffickers.

The goal of the operation was to regain control of territory controlled by Mexico's drug cartels. EFE