One of the guns might have contributed to the death of a U.S. agent, The Hill newspaper said.
Sen. Charles Grassley, R-Iowa, is demanding the U.S. Justice Department respond to queries about the "Gun Runner" program. The program authorized the sale of guns to people acting as straw purchasers for Mexican drug cartels, eventually allowing 1,300 firearms to reach the gangs, The Hill said.
"Gun Runner" and a separate operation, "Fast and Furious," was supposed to dismantle the cartel's gun-smuggling routes that get assault rifles from the United States into Mexico. The Hill said government agents hoped by letting the straw purchasers buy large quantities of weapons, they could trace the firearms to the cartel members.
But government whistle-blowers allege officials lost track of the guns, the report said.
Two of the firearms from the operation were found in Arizona at the scene of a gun battle, The Hill said. The gun battle killed Border Patrol Agent Brian Terry, but U.S. officials have not said whether the round that struck him came from the guns the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives was supposed to be tracking.
U.S. officials refuse to provide Grassley with documents, saying prosecutions are pending. But Grassley has been working House Oversight and Government Reform Committee Chairman Darrell Issa, R-Calif., who has subpoena power, and has gotten some documents.
U.S. Attorney General Eric Holder has said he was unaware of the operation, and has started an internal investigation.