Mexico's war on drug cartels more resembles a military campaign than law enforcement, with federal troops taking on heavily armed traffickers, the New York Times reported Jan. 22.

Battles have included troops firing 50-caliber machine guns mounted on jeeps and Mexican Navy jets flying reconnaissance missions, with clashes in cities like Tijuana and Rio Bravo. Often, the fight pits the federal authorities against both the drug cartels and corrupt police. "You cannot count on the local police," said one federal official in Reynosa. "The problem lies in the state police. They are completely at the service of these guys."

Some local residents applaud the crackdown, while other complain that it has discouraged U.S. visitors to border towns, and some collaborators act as lookouts for the drug gangs.

Among the main targets of the federal troops are the Gulf Cartel and their paramilitary Zeta gunmen, many of whom have military backgrounds.

Mexican President Felipe Calderon has sent 6,000 troops into the drug-plagued state of Tamaulipas alone. Officials have been surprised that the drug gangs have often chosen to stand and fight when confronted, and police and troops face the constant threat of ambush and assassination. Some of the violence has spilled over the border into the U.S.

"The Zetas are defying the state," said Jorge Chabat, a narcotics trafficking expert at the Mexican research group CIDE. "This operation in the north of Mexico in recent days has no precedent."