In a case aimed at stemming the flow of U.S. weapons to the Mexican drug war, federal authorities indicted 20 men Tuesday on charges of buying an estimated 700 weapons in Arizona and conspiring to transfer them across the border, chiefly to the Sinaloa drug cartel.

The arrests, carried out by at least 100 federal agents, began early Tuesday, the latest crackdown targeting an international trafficking network that authorities say has seen as many as 60,000 weapons seized in Mexico and traced to U.S. sources.

“The massive size of this operation sadly exemplifies the magnitude of the problem: Mexican drug lords go shopping for war weapons in Arizona,” Dennis Burke, U.S. attorney in Arizona, said in a statement.

Officials at the federal Bureau of Alcohol, Tobacco, Firearms and Explosives said the case demonstrates the need to include long-barreled weapons in the requirement for gun sellers to report multiple weapon sales to a single buyer. The proposal has been opposed by the National Rifle Assn. and many gun owners as an inappropriate reach of federal authority.


Gun advocates say many of the weapons in the hands of Mexican drug traffickers were acquired from weapons stocks officially supplied by the U.S. government to Mexico and other Latin American countries.

The case involves the relatively common use of “straw purchasers,” legal residents of the state who buy the weapons from licensed gun dealers and certify that they are for their own use, but end up selling the guns to the drug cartels.

None of those charged in the indictments are licensed gun dealers. But the indictments identify a number of Arizona dealers that legally supplied large quantities of weapons to individual buyers, often in a single day.

One of the defendants, Uriel Patino, for example, purchased 26 AK-47 rifles from Lone Wolf Trading Co. in Glendale, Ariz., on March 26; 10 more on June 2 from the same outlet; 16 on July 8; and 12 on Aug. 5 — in addition to purchasing a number of other weapons.


In all these cases, according to the indictment, Patino signed a federal form certifying that he was not buying the weapons for someone else, a requirement that is prominently featured on Lone Wolf’s website.

But on Aug. 8, federal agents found all 12 of the AK-47s purchased Aug. 5 concealed in a stove and a television in what was an apparent attempt to smuggle them into Mexico through the border crossing at Lukeville, Ariz.

A few months earlier, on Feb. 20, law enforcement agents intercepted an Isuzu Rodeo on the Tohono O’odham Nation territory in southeastern Arizona that was loaded with 37 AK-47s purchased by Patino between Jan. 15 and Feb. 13.

The federal firearms bureau announced in December that it was proposing to require an estimated 8,500 gun dealers along the southwestern U.S. border to provide notice of multiple rifle sales, but gun advocates have said it is an attempt to blame lawful gun dealers for border enforcement problems and the violence in Mexico.


“This is just a shallow excuse to engage in a sweeping firearms registration scheme,” Wayne LaPierre, the NRA’s chief executive and executive vice president, wrote on the organization’s website.

Tom Mangan, spokesman for the firearms bureau in Phoenix, said officials are hopeful the regulation will go through.

“It’s not prohibiting; it’s not infringing upon a purchaser’s right to buy guns,” he said.

kim.murphy@latimes.com