South of the border, war is raging with guns mostly supplied by merchants in the United States.

The Government of Mexico has estimated that almost 50,000 people have been killed since 2006, a toll that has made its top officials irate about the persistent flow of weapons south. Some law enforcement officials in the U.S. government share the Mexican’s concern, but their attempts to stanch the flow by obtaining better intelligence about it have badly singed their fingers.

The notorious “Fast and Furious” operation by the Bureau of Alcohol, Tobacco and Firearms — one in a string of attempts over a nearly decade-long period to tag and closely monitor the movement of individual arms — blew up when two of the weapons being tracked were used to kill a U.S. border patrol agent in 2010.

Republicans in Congress seized on the issue, holding multiple hearings last year. Acting ATF Director Kenneth Melson was reassigned. The Phoenix U.S. attorney who oversaw the operation also resigned, and Republicans called for the resignation of Attorney General Eric Holder. And President Obama has been largely hands off on the gun issue, treating it as the political third rail that is best to be ignored, or at least carefully walked around.

Into this politically charged environment, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) released a first-of-its-kind report on Thursday that nonetheless attempts to assess the proportional distribution — if not the scope — of the arms flowing to drug cartel operatives.

It confirmed that a majority of the weapons being used by the Mexican drug cartels to kill police, criminals, and civilians alike have come from inside the United States. Precisely, of the 99,691 weapons traced from Mexico between 2007 and 2011, 68,161 were manufactured or imported from the U.S. — over 68 percent. Because the data only reflect arms that are captured by Mexican law enforcement agencies, they depict only a subset of all those that flow south.

The data also showed the U.S. arms’ contribution is becoming more malignant: Criminals using U.S. weapons have been moving from handguns to rifles with detachable magazines, weapons with far greater destructive ability in conflicts with government forces. The percentage of traced guns that were rifles went from 28.2 percent in 2007 to 43.3 percent in 2011, while the percentages for pistols, revolvers and shotguns declined.

The flow of U.S. weapons to foreign countries isn't constrained just to Mexico. Over the five years studied in the report, over 99 percent of the weapons seized for tracing in Canada, for example, were of U.S. origin. Of the five countries studied in the Caribbean for 2011 alone, the largest percentage of weapons with a U.S. origin came from The Bahamas (94 percent), followed by the Dominican Republic (81.3 percent), Jamaica (80.8 percent), Barbados (60 percent) and Trinidad and Tobago (43.3 percent); the majority of weapons seized for tracing were handguns.

But Mexico remains the more volatile situation. After all, there aren't civilians being gunned down in the streets of Vancouver. Some of the most powerful weapons to show up in Mexico were first imported in a stripped-down condition into the United States, and then modified by domestic gun dealers before being transported.

The data has been seized upon by advocates of stricter gun controls in the United States. In a press release, Sen. Diane Feinstein (D-CA) said the new data "makes it very clear that we need to increase our efforts to starve the supply of American weapons that arm Mexico's brutal drug trafficking organizations." ATF was required to release the gun recovery data due to a provision authored by Feinstein as part of last year's Commerce, Justice, and Science Appropriations bill.

The reports form the most comprehensive long-term data available for guns that have been traced through ATF's National Tracing Center. A report done in 2009 by the Government Accountability Office found that 87 percent seized by Mexican authorities and traced over the previous five years were from the United States — a higher figure that suggests U.S. law enforcement efforts to root out trafficking may now be having a modest impact.

The National Rifle Association’s Institute for Legislative Action, a group funded partly by gun manufacturers, did not have an immediate comment.