Five men were found asphyxiated in a car Saturday in the eastern part of the city, according to the Baja California state Attorney General's Office. The men were beaten and had their hands bound.
The bodies of two beheaded men were found wrapped in blankets on a road elsewhere in the city, the office said. The heads were in black plastic bags nearby.
A piece of cardboard left by the bodies read: "These are the bricklayer's people." On Monday, a message found with 12 bodies next to a Tijuana elementary school threatened "all of those who are with 'The Engineer."'
State prosecutor Rommel Moreno has blamed the violence on warring leaders within the Arellano Felix drug gang. More than 400 people have been killed in drug-related violence in the city across from San Diego this year, including at least 49 this week.
On Friday night, two men were found shot to death in the same empty lot near the elementary school where the 12 bodies were found Monday.
Execution-style killings, beheadings and shootouts have soared across Mexico since the army and federal police intensified their fight against the drug trade nearly two years ago.
Gunmen Saturday killed the mayor of Ixtapan de la Sal, a resort town southwest of Mexico City. Salvador Vegara was in a car with two other people when the gunmen opened fire from another vehicle, said Moises Gonzalez, a spokesman for Mexico state Attorney General's Office. The two other people were injured.
In the southern city of Oaxaca, four banners purportedly signed by the Gulf Cartel blamed another drug gang, La Familia, for a Sept. 15 grenade attack that killed eight people during Independence Day celebrations in another Mexican state capital, Morelia.
Police earlier arrested three alleged Gulf Cartel hit men accused of throwing the grenades into crowds of revelers. Messages in the name of La Familia have blamed the Gulf Cartel for the attack.
Police quickly took down the banners. Oaxaca state police commissioner Jorge Quezadas said they were handed over to federal prosecutors for investigation.