The U.S. was the source of at least 70% of 29,284 firearms recovered by authorities in Mexico in 2009 and 2010, according to new U.S. government figures.
The statistics from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives are expected to add to controversy over the U.S. role in fueling drug-cartel violence in Mexico, which has killed more than 40,000 people since 2006.
U.S. gun-rights groups long have disputed assertions by the U.S. and Mexican governments that trafficking from the U.S. is a major source of weapons in the cartel wars. They have contended the majority of Mexican guns come from Russia, China and elsewhere.
The controversy was fueled in recent years when U.S. officials backed off earlier claims that up to 90% of firearms recovered in Mexico were of U.S. origin.
The findings come as the ATF defends itself against congressional critics for its Fast and Furious gun-tracking operation, which lawmakers say inadvertently eased trafficking of weapons to cartel gangs.
Lawmakers say the agency lost track of firearms and allowed 2,500 weapons into the hands of suspected traffickers. A weapons cache found in Ciudad Juarez, Mexico, in April included five firearms that the ATF has now linked to suspects in the Fast and Furious operation., The Wall Street Journal reported Wednesday.
The ATF figures show that 21,313 firearms recovered in Mexico in 2009 were submitted for tracing by the agency. Of these, 10,945 were manufactured in the U.S. and 3,268 were imported into the U.S. from third countries before ending up in Mexico. The origin of 7,100 firearms couldn't be determined.
Of 7,971 firearms recovered in Mexico in 2010 and traced by ATF, 4,186 were manufactured in the U.S. and 2,105 were imported into the U.S. The origin of 1,680 firearms couldn't be determined.
Collectively, the data show that of the 29,284 firearms recovered in Mexico in 2009 and 2010 and submitted to the ATF for tracing, 20,504 or 70% passed through the U.S. at some point. The period is the most recent for which data are available.
The ATF said it traced the guns based on information provided by Mexican authorities. The Mexican government doesn't submit every firearm it recovers for tracing.
Mexico has strict restrictions on gun ownership, with most legitimate sales processed through one store on a military base near Mexico City.
ATF Acting Director Kenneth Melson provided the data to Sen. Dianne Feinstein (D., Calif.), who requested the information. It represents the first such analysis to be made public by the agency. The law limits how ATF can share the data it obtains from tracing guns used in crimes.
Sen. Feinstein, chairman of the Senate Caucus on International Narcotics Control, said in a May letter to Mr. Melson that "military-style weapons are arming Mexico's brutal drug trafficking organizations at an alarming rate. Releasing data on firearms recovered in Mexico that originate in the United States will ensure that the American public and policymakers are aware of the severity of this problem."
The figures prompted strong reactions from advocates on both sides of the U.S. gun-control debate.
Wayne LaPierre, executive vice president of the National Rifle Association, said he doubted the ATF figures. He said given the ample resources of drug cartels, traffickers easily import weapons from Russia, China, and Central America, rather than risk trying to smuggle firearms from the U.S. "I think all these numbers are phonied up for politics," Mr. LaPierre said in an interview. "The law enforcement people I talk to tell me this doesn't make sense."
Dennis Henigan, vice president of Brady Center to Prevent Gun Violence, said: "The traffickers are following the path of least resistance. They're going to American gun shops, exploiting the permissive U.S. gun laws. It's beyond time for the United States to strengthen its gun laws and shut down the trafficking."