An arsenal of assault rifles and other weapons seized by police in Mexico has been traced to a US government program that intentionally allowed guns to be smuggled into Mexico.

The Wall Street Journal reported Thursday that the weapons discovered in a raid last April in Ciudad Juarez, the Mexican border town which is the front line of the government’s US-backed drug war, “included two dozen AK-47-style rifles, three antiaircraft machine guns, dozens of grenades and more than 26,000 rounds of ammunition.”

At least five of the AK-47s—Romanian-made—have been traced to guns run across the border as part of a “sting” operation conducted by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).

The ATF, a sub-agency of the US Justice Department, is officially charged with preventing “the illegal use and trafficking of firearms.” Yet, under the Mexican sting operation, dubbed “Fast and Furious,” it oversaw the illegal smuggling of some 2,500 weapons across the border and into the hands of Mexican drug gangs, according to government sources including agency whistle-blowers. This flow of arms has included many hundreds of AK-47s and Barrett .50 caliber military assault rifles.

The weapons are believed to have played a significant role in fueling the carnage unleashed by the US-backed drug war that is being carried out by the Mexican government of President Felipe Calderón. Since 2006, when Calderón deployed troops to combat drug trafficking, some 40,000 Mexicans have been killed in the violence.

Guns allowed into Mexico under the ATF program have been used in the killing of a US Border Patrol agent and in a recent attempt to shoot down Mexican military helicopters.

While many thousands have demonstrated in Mexico against the drug war and against the flow of weapons across the border, the Calderon government has been noticeably silent about the growing scandal surrounding the ATF’s “Fast and Furious” sting operation.

Republican Representative Darrell Issa of California, who chairs the House Oversight Committee, has scheduled public hearings on “Operation Fast and Furious” next week in Washington. Among those expected to testify are ATF whistleblowers who have been working with congressional investigators. Republicans in Congress have charged the Obama administration’s Justice Department with stonewalling the investigation.

US Attorney General Eric Holder has named a Justice Department inspector general to conduct an in-house probe of the sting operation. Both he and Homeland Security Secretary Janet Napolitano claim they knew nothing about “Fast and Furious” until it was exposed by media reports.

Government officials have claimed that “Fast and Furious” was the ATF’s response to an audit of the agency that criticized it for failing to pursue major traffickers instead of small-scale gun runners. However, the immense volume of weapons allowed into Mexico under the operation has raised serious questions as to the aims of the US government—including speculation over whether its intention was to fuel the drug war or to favor one Mexican drug cartel over another.