Parts of northern Mexico appear to be under virtual siege, with drug gangs pinning up hit lists across one city, showing names of police officers it wants to murder.
An unusual chill has fallen Chihuahua City, just across from El Paso on the Texas border, after authorities said they found banners attached to bridges displaying a list of 21 police officers targeted for assassination, reportedly written by a gang called Gente Nueva (New People).
Violence spawned by drug trafficking gangs who are at war both with each other and law enforcement officers has escalated to the point where towns and cities in the north are operating, in effect, under curfew.
Residents in Ciudad Juarez, also in Chihuahua State, stayed mostly in their homes last weekend after a mystery email surfaced warning of an impending bloodbath – with shopping malls and nightclubs listed as likely targets of gunfire.
In the end, the city merely endured a roughly normal level of gang-related killings, including at least six murders on Saturday, with two police officers among the victims, and eight killings on Friday.
Such warnings are not taken lightly. In January, unidentified gangs pinned a similar list to a police memorial in Juarez. So far, 17 police officers on that list have been killed.
The recent surge of gangland killings has been attributed in part to a crackdown on the cartels launched by President Felipe Calderon almost as soon as he was sworn into office in December 2006.
There is no sign that the Calderon government intends to back down, in spite of the violent response, which included the assassination three weeks ago of the federal police chief, Edgar Millan, in the grounds of his home in Mexico City. Juarez has lost its chief and deputy chief of police in recent weeks. The former resigned and the latter was mown down by machine-gun fire.
Mr Calderon has deployed about 25,000 troops and federal police to the mountainous area in the country's north-west in an attempt to loosen the grip of the cartels. He has also purged police officers accused of siding with the traffickers and disarmed whole police departments deemed to have been infiltrated.
The cost has been enormous. Last week, federal authorities announced 1,400 people have been killed in the drugs war this year already, up 47 per cent from the same period in 2007.
The recent convulsions have been taken by some as a sign that the crackdown is working. The government believes that drug trafficking routes have been disrupted and cartel revenues diminished. For the first time, meanwhile, captured cartel leaders who, in the past have been able to conduct business as usual from behind bars, are now being extradited to the United States to tand trial. But sustaining the effort is becoming harder, not least because of plummeting police morale. Many officers continue to face a choice between risking their lives for scant monetary reward from the government or succumbing to the promise of big pay-offs and physical security if they side with the gangs.
In a remarkable sign of the difficulties they face, three Mexican police chiefs working in northern Mexican towns have crossed the border into the United States in the past four weeks and requested asylum.
The US is not a casual observer of this strife. In its latest International Narcotics Control report, the State Department confirms that 90 per cent of cocaine consumed in the US is imported from Mexico. The report offers praise, noting that Mexico has "made unprecedented efforts and achieved unprecedented results in attacking the corrosive effects of drug trafficking and consumption."
But Mexican officials, far from being flattered, are increasingly frustrated that the so-called Merida initiative negotiated last year by Mr Calderon and President George Bush that was meant to extend $500bn (£250bn) annually in US aid to combat the cartels, notably with the provision of helicopters, fixed-wing aircraft and other equipment, has so far failed to win passage through the US Congress.
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