The Mexican armed forces and prosecutors have suffered at least 28 gunfire attacks on helicopters in the five years since the government launched an offensive against drug cartels, according to official documents made public Monday.
The attacks show the increasing ferocity of Mexico's drug gangs, and also suggest support for what the Mexican government has said in the past: that 2010 may have been the worst year for the upward spiral in violence.
In the first two years of the drug war, reporting government agencies such as the air force, navy and Attorney General's Office reported no chopper attacks. But in 2008, four helicopters were hit by gunfire, wounding at least one officer aboard.
In 2009, bullets struck six government helicopters in the rotors, side doors or motor compartments. All the craft were apparently able to land safely.
However, 2010 was the worst year for helicopter attacks, with 14 hit and one crew member wounded. Some craft had as many as seven bullet holes in them when they landed, with rounds going through windshields, fuselages, rotors and even landing gear.
In 2011, only three helicopters were hit by gunfire, but the number is almost certainly higher. The federal police refused to release data on attacks on its craft, but publicly acknowledged that on May 24, suspected cartel gunmen opened fire on a federal police chopper, hitting two officers and forcing the craft to land, though officials insisted it had not been shot down.
Federal police said the pilot in that incident landed "to avoid any accident." The Russian-made Mi-17 touched down about 3.5 miles (6 kilometers) from the shooting scene in the western state of Michoacan. Two officers aboard suffered non-life-threatening wounds.
Mexico has long used helicopters in anti-drug operations. While security forces have updated their helicopter fleet in recent years, they have also retired some older craft, so the total number of choppers would not account for the variation in attacks.
The newspaper Milenio originally requested the attack reports through a freedom of information request, and the reports were independently accessed by The Associated Press.
Mexican drug gangs have long strung steel cables around opium and marijuana plantations to try to bring down police and military helicopters. In 2003, in what prosecutors said was the first fatal attack of its kind by drug traffickers in Mexico, gunmen guarding an opium-poppy plantation shot down two police helicopters, killing all five agents aboard.
But those attacks were infrequent compared to what's occurred since 2008.
Overall drug-related killings rose 11 percent in the first nine months of 2011, when 12,903 people were killed, compared to 11,583 in the same period of 2010, the office said. But the Attorney General's Office found one small consolation: "It's the first year (since 2006) that the homicide rate increase has been lower compared to the previous years."
Drug-related killings jumped by 70 percent for the same nine-month period of 2010 compared to January to September 2009, when 6,815 deaths were recorded.
The carnage continued Monday, when seven gunmen were killed in a pre-dawn shootout with police on a highway in the city of Cuernavaca, south of Mexico City.
A federal police officer was recovering from a gunshot wound to the foot following the confrontation.
The prosecutors' office in the central Mexican state of Morelos says the gunmen belonged to an organized crime gang, but did not say which one.
"Organized crime" in Mexico generally refers to drug cartels, and remnants of the Beltran Leyva cartel have been fighting for control of Cuernavaca.
Prosecutors said the gunmen were traveling in three stolen vehicles when police confronted them early Monday.