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.
The shooting Monday suggested that Colombian-style drug violence may be spreading to Mexico. Although drug-eradication flights have been fired on before, none had been shot down.
Four of the five agents who died burned to death in the crash. The fifth victim died of injuries. None had bullet wounds, although the helicopters were riddled by automatic-weapons fire. All of the victims were police pilots or investigators.
The attack near Tlapa, 130 miles south of Mexico City, was among the battle-style tactics used by drug growers to protect their opium plantations.
At least five times in the last year, they have strung steel cables across drug fields to try to snare the rotors of crop-spraying helicopters, said Estuardo Mario Bermudez, Mexico's top anti-drug prosecutor.
Although most heroin sold in the United States comes from Colombia, opium poppy cultivation has grown rapidly in Mexico. U.S. officials have said Mexico's clandestine poppy fields are among the best-hidden in the world, often in mountaintop jungle clearings.