Gunmen are turning innocent bystanders into targets in what appears to be a new phase to the violence

Fifteen people killed in a car wash, 14 massacred at a teenager's birthday party, 13 shot dead at a drug rehabilitation centre, seven mowed down in the street, four factory workers killed on a bus and nine police officers killed in an ambush.

Even by Mexican drug war standards, it has been a hellish week, crystallising the burgeoning sense that the violence has reached a new stage and fuelling dissatisfaction with the cost and efficacy of President Felipe Calderón's military-led offensive against the cartels.

The massacres have shocked Mexicans so deeply less because of the number of victims than the fact that most of the men, women and children killed were obviously unconnected to any of the cartels fighting each other around the country. None belonged to the federal forces involved in the government's offensive either.

The only obvious link between the different massacres, regardless of the specific motives prompting each attack, was the way the different groups of gunmen involved turned anybody who happened to be at the scene into their target.

Survivors of the birthday party bloodbath, which happened in a private home in the border city of Ciudad Juárez shortly after midnight last Saturday, said their assailants first demanded to know the whereabouts of a man nicknamed The Mouse. When they didn't get a satisfactory response they opened fire indiscriminately.

Juarez was also the site of Thursday's attack on a bus full of factory workers going home after a late-night shift. An armed commando reportedly started shooting after the driver didn't immediately stop when ordered.

Initial investigations into the assault on the El Camino rehabilitation centre in Tijuana pointed to a possible retaliation for the seizure of 134 tonnes of marijuana last week. The gunmen lined up the addicts face down on the floor then emptied their semi-automatic assault rifles over their victims.

Ten of those killed at the car wash in the western city of Tepic on Wednesday morning were also recovering addicts who were employed there, although witnesses suggested the more likely target was the owner. Either way, the attack was equally random, and in a city only recently drawn into the drug war's messy patchwork of overlapping conflicts that have killed more than 28,000 people since Calderón launched his crackdown nearly four years ago.

The murder of six young men in Mexico City's crime-ridden Tepito barrio was the only one of this week's massacres in which the victims might have been connected with drug trafficking. They also might not have been.

The week's violence was rounded off when unidentified gunmen ambushed a convoy of five police vehicles in the western state of Jalisco on Thursday, killing nine officers and leaving one missing. The 20 officers in the convoy were outnumbered by the attackers, who were riding in about 10 SUVs and used grenades and assault rifles.

The 10 officers who survived the attack fought an hours-long battle with the gunmen, and several were wounded.

Together with the more routine daily litany of lesser-scale gun fights and executions, the total drug wars death toll for October was estimated by the Milenio television channel at around 1,000.

"This kind of violence has a natural evolution," Edgardo Buscaglia, an international organised crime expert, said of the escalating violence and the wave of attacks against innocent people. He has argued from the start that the Calderón strategy is counter-productive unless the political elite purges itself of narco influence. If they don't do this soon, he warned, "Mexico is on the road to turning into a kind of Afghanistan".

Critics of the government strategy are planning protests to coincide with Monday's day of the dead celebrations. As well as a march through the capital dressed in black, they are preparing a version of the traditional altar for the souls of the departed dedicated to Mexico.

"I know that there is uncertainty and pain in our society," Calderón said midweek, intent on showing he was not indifferent to the malaise. "But I say to you, with absolute certainty, that it is possible to defeat the criminals."