Mexico City: At least 21 people, including a 12-year-old girl and other innocent citizens, have been killed by warring drug gangs since Thursday in the western state of Sinaloa, in one of the worst spasms of violence in memory in a region long conditioned to narcotics-related savagery.

A wave of mayhem that began with the audacious daytime shooting deaths of a dozen people in the capital of Culiacan continued during the weekend and into Monday.

The deaths of innocents, including the 12-year-old girl who had just left a party, has terrified the public and left many people questioning the effectiveness of the federal government's ongoing crackdown on drug trafficking.

Carnage

"Sinaloa Bloodbath" read a headline from El Sol de Sinaloa, a daily newspaper whose website on Monday carried a photo of corpses slumped in the back of a bullet-riddled pickup truck.

Authorities were sorting through the carnage in Sinaloa as the body count continued to rise Monday. But law enforcement and Mexican media accounts provide a picture of the relentless violence:

On Thursday, gunmen in Culiucan shot dead six people inside an auto repair shop and three more outside.

Early Saturday morning in Cuilican, rival traffickers shot it out with automatic weapons and bazookas in a neighbourhood in the northern part of the city.

Police reported no deaths or injuries in that 15-minute clash, but photos from the scene show the pavement littered with heavy-calibre shell casings and homes scarred with bullet holes.