(CNN) -- Federal agents can't account for more than 1,400 guns after a widely criticized operation aimed at tracing the flow of weapons to Mexican drug gangs, sources with knowledge of the investigation tell CNN. Of 2,020 guns involved in the Bureau of Alcohol, Tobacco, Firearms, and Explosives probe dubbed "Operation Fast and Furious," 363 have been recovered in the United States and 227 have been recovered in Mexico. That leaves 1,430 guns unaccounted for, the sources said. The ATF operation was intended to build cases against Mexican drug cartels by allowing firearms to go from the United States into Mexico. The hope was by tracing the guns in Mexico, agents would be able to determine the structure of various cartels and then bring them down.
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"Operation Fast and Furious" involved more than 2,000 guns, sources tell CNN
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Fewer than 600 have been recovered in the United States and Mexico, they say
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The operation has been sharply criticized by members of Congress
In Mexico, the operation drew sharp criticism from top officials, who have long said that @placeholder weapons are fueling the country's bloody drug war.