TIJUANA, Mexico (AP) -- Police have found nine more bodies dumped around the Mexican border city of Tijuana, where nearly 50 people have been killed in a week of violence related to the drug trade.

Municipal police found five of the bodies Saturday between two small shopping centers in the eastern part of the city. The people had been beaten, and their hands were bound.

The bodies of two beheaded men were found wrapped in blankets on a road elsewhere in the city, according to the Baja California state Attorney General's Office. 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, California, 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.

In the southern city of Oaxaca, four banners purportedly signed by the Gulf Cartel blamed another drug gang, La Familia, for a September 15 grenade attack that killed eight people during Independence Day celebrations in another Mexican state capital, Morelia.

Police 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.