ZIHUATANEJO, MEXICO, AND MEXICO CITY — It was a brazen assault, not just because it targeted the city's police station, but for the choice of weapon: grenades.
The Feb. 21 attack on police headquarters in coastal Zihuatanejo, which injured four people, fit a disturbing trend of Mexico's drug wars. Traffickers have escalated their arms race, acquiring military-grade weapons, including hand grenades, grenade launchers, armor-piercing munitions and antitank rockets with firepower far beyond the assault rifles and pistols that have dominated their arsenals.
Most of these weapons are being smuggled from Central American countries or by sea, eluding U.S. and Mexican monitors who are focused on the smuggling of semiauto- matic and conventional weapons purchased from dealers in the U.S. border states of Texas, New Mexico, Arizona and California.
The proliferation of heavier armaments points to a menacing new stage in the Mexican government's 2-year-old war against drug organizations, which are evolving into a more militarized force prepared to take on Mexican army troops, deployed by the thousands, as well as to attack each other.
These groups appear to be taking advantage of a robust global black market and porous borders, especially between Mexico and Guatemala. Some of the weapons are left over from the wars that the United States helped fight in Central America, U.S. officials said.
"There is an arms race between the cartels," said Alberto Islas, a security consultant who advises the Mexican government.
"One group gets rocket-propelled grenades, the other has to have them."
There are even more ominous developments: Authorities reported three thefts of several hundred pounds of blasting material from industrial explosives plants in Durango during a four-day period last month. Authorities believe the material may have been destined for car bombs or remotely detonated roadside devices, which have been used with devastating effect in Iraq, killing more than 1,822 members of U.S.-led forces since the war there began nearly six years ago.
The Mexican army has recovered most of the material, and there has been no reported use of such devices.
Grenades or military-grade weapons have been reported in at least 10 Mexican states during the last six months, used against police headquarters, city halls, a U.S. consulate, TV stations and senior Mexican officials. In a three-week period ended March 6, five grenade attacks were launched on police patrols and stations and the home of a commander in the south-central state of Michoacan. Other such attacks occurred in five other states during the same period.
At least one grenade attack north of the border, at a Texas nightclub frequented by U.S. police officers, has been tied to Mexican traffickers.
How many weapons have been smuggled into Mexico from Central America is not known, and the military-grade munitions are still a small fraction of the larger arsenal in the hands of narcotics traffickers. Mexican officials continue to push Washington to stem the well-documented flow of conventional weapons from the United States, as Congress holds hearings on the role those smuggled guns play in arming Mexican drug cartels.
There is no comprehensive data on how many people have been killed by heavier weapons.
But four days after the assault on the Zihuatanejo police station, four of the city's officers were slain in a highway ambush six miles from town on the road to Acapulco. In addition to the standard AK-47 and AR-15 assault rifles, the attackers fired at least six .50-caliber shells into the officers' pickup. The vehicle blew up when hit by what experts believe was a grenade or explosive projectile. The bodies of the officers were charred.
"These are really weapons of war," said Alberto Fernandez, spokesman for the Zihuatanejo city government. "We only know these devices from war movies."
U.S. law enforcement officials say they detected the smuggling of grenades and other military-grade equipment into Mexico about a year and a half ago, and observed a sharp uptick in the use of the weapons about six months ago.
The Mexican government said it has seized 2,239 grenades in the last two years, in contrast to 59 seized over the previous two years.
The enhanced weaponry represents a wide sampling from the international arms bazaar, with grenades and launchers produced by U.S., South Korean, Israeli, Spanish or former Soviet bloc manufacturers. Many had been sold legally to governments, including Mexico's, and then were diverted onto the black market. Some may be sold directly to the traffickers by corrupt elements of national armies, authorities and experts say.
The single deadliest attack on civilians by drug traffickers in Mexico took place Sept. 15 at an Independence Day celebration in the central plaza of Morelia, hometown of President Felipe Calderon and capital of Michoacan. Attackers hurled fragmentation grenades at the celebrating crowd, killing eight people and wounding dozens more.