A gun from the failed U.S. operation known as "Fast and Furious" turned up at the scene of a shootout between Mexican authorities and alleged cartel gunmen last month, according to CNN.

U.S. officials told CNN at least one AK-47-style gun that could be traced back to the failed gun-walking scheme was found at the scene.

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The shootout on Dec. 18 left five alleged cartel members dead in Puerto Peñasco, a popular tourist site in Mexico.

The now-defunct Fast and Furious program began in 2009 and was run by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). Agents allowed low-level weapons purchasers to cross the Mexican border in an attempt to expose trafficking routes used by Mexican cartels. But the agency ultimately lost track of some weapons, including two found at the scene of the killing of a border patrol agent in 2010.

The ATF acknowledged that weapons from the operation would likely continue to turn up at crime scenes.

“ATF has accepted responsibility for the mistakes made in the Fast and Furious investigation and at the attorney general's direction we have taken appropriate and decisive action to ensure that these errors will not be repeated,” the bureau said in a statement to CNN.

"And we acknowledge that, regrettably, firearms related to the Fast and Furious investigation will likely continue to be recovered at future crime scenes," it added.

House Oversight Committee Chairman Darrell Issa (R-Calif.) and Sen. Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE (R-Iowa) led the congressional investigation into the program.

Grassley, in a statement to CNN, expressed regret that no one in the administration had yet been held accountable.

“Unfortunately, guns from Fast and Furious will be found in operations like this for years to come," he said.