The carnage has cut a wide arc through Mexico and underscored the gangsters' brazen willingness to take on military troops and Mexican federal police in direct combat.

Among this week's victims were 12 federal police officers ambushed Monday by presumed gangsters in western Michoacan state and three others bushwhacked in northern Chihuahua state. Army troops shot it out with gunmen Tuesday in Taxco, a tourist mecca 100 miles south of Mexico City, killing 15 alleged criminals.

"The difference now is that the criminals and security forces are clashing more frequently," said Raul Benitez-Manaut, a national security analyst. "The criminals are directly challenging the government."

Heavy violence

The conflict constitutes the most serious organized violence since the Mexican Revolution began a century ago. And it has become one of the largest armed conflicts in the world.

For example, the more than 2,700 people murdered last year in Ciudad Juarez outstrips the combat fatalities suffered by civilians and Allied troops in Afghanistan during the same period, according to statistics compiled by United Nations and private analysts.

On Wednesday, investigators recovered the bodies of five city police officers butchered in a Monterrey suburb. Dozens of policemen have been killed in the Monterrey area in recent months.

The governor of Nayarit, the state that includes the small beach resorts outside Puerto Vallarta popular with U.S. tourists, cancelled the remainder of the school year. Parents had panicked amid rumors that gangsters were going to target drug rivals' children following gun battles in the state capital that killed 30 people during the weekend.

Gov. Ney Gonzalez called on Calderón to send federal troops to Nayarit, which hadn't suffered significant gang violence until recently.

"Society asks the government to act, and we are going to act," Gonzalez told the newspaper Universal on Wednesday. "This is our territory. We are going to protect and defend it."

Calderón cancelled a public event Wednesday morning to meet with his national council.

Easy access to weapons

In a nationally televised address Tuesday, he again blamed much of the unrest on demand for illegal drugs in the United States and on Mexican gangsters' easy access to assault weapons bought in Texas and other U.S. states.

But Calderón also argued that government officials' historical connivance with the gangs was largely responsible for the power they have accumulated. He said the crackdown is essential as gangs increasingly sell drugs to Mexican consumers, extort businesses and private citizens and challenge the government's control.

Underworld warfare has killed more than 23,000 Mexicans since Calderón launched his crackdown upon taking office in December 2006. At least 1,200 people have been killed so far this year in Juarez, Mexico's most violent city and one of the most dangerous in the world.

Though soldiers and the federal police have clashed with the gangsters, Mexico until now had essentially suffered through a civil war among the criminal gangs.

In Calderón's home state of Michoacan, the La Familia criminal organization has fought Zetas and other rivals as well as the federal police and army. Officials also blame La Familia gunmen for the ambush Monday that killed 12 federal policemen.

Cartels at war

Along the cities bordering South Texas and into Monterrey, the so-called Gulf Cartel has gone to war with the Zetas, paramilitary gunmen who once worked for it.

Rivalries between former underlings of drug boss Arturo Beltran-Leyva, who was killed by Mexican marines last December, have fueled the killing in that city as well as Cuernavaca, Acapulco and the suburbs of Mexico City.

Six addicts were murdered at a drug rehabilitation center in Ciudad Juarez, bordering El Paso on Wednesday. Another 19 addicts were killed at another center in the Chihuahua state capital June 10.

Analysts say addicts also are members of street gangs allied with warring trafficking organizations and, so, are targeted.

On Monday, 28 inmates were butchered by gang rivals at a state prison in the Pacific port city of Mazatlan.

And the bodies of 18 men and two women were dumped on streets near the Gulf Coast city of Tampico on Friday morning.

"They are still lacking important elements of a successful strategy," Benitez-Manaut, the analyst, said of Mexican security forces. "But as long as the gangsters are killing each other the government is winning."

dudley.althaus@chron.com