Washington ? The Justice Department replaced three officials Tuesday who played critical roles in a flawed law enforcement operation aimed at major gun-trafficking networks on the Southwest border.

The department announced that the acting director of the Bureau of Alcohol, Tobacco, Firearms and Explosives and the U.S. attorney in Arizona had resigned and an administration official said a prosecutor who worked on the operation was reassigned to civil cases.

The operation, known as Fast and Furious, was designed to track small-time gun buyers at several Phoenix-area gun shops up the chain to make cases against major weapons traffickers. It was a response to longstanding criticism of ATF for concentrating on small-time gun violations and failing to attack the kingpins of weapons trafficking.

A congressional investigation of the program has turned up evidence that ATF lost track of many of the more than 2,000 guns linked to the operation. The Justice Department inspector general also is looking into the operation at the request of Attorney General Eric Holder.

The operation has resulted in charges against 20 people and more may be charged.

Kenneth Melson will be replaced as ATF’s acting chief by B. Todd Jones, the U.S. attorney in Minnesota.

With Republicans in Congress and the department bickering over the investigation, Melson finally testified recently to Hill investigators in private. He said his department superiors “were doing more damage control than anything” and trying to keep the controversy away from top officials.

Also leaving was Dennis Burke, U.S. attorney in Arizona, whose office was deeply involved in Operation Fast and Furious. Burke will be replaced on an acting basis by his first assistant, Ann Scheel.

In a related change, the line prosecutor in the U.S. Attorney’s Office in Phoenix who worked on the Fast and Furious investigation, Emory Hurley, was reassigned from criminal cases to civil case work, according to an administration official, who spoke on condition of anonymity about the personnel matter.

The moves are the latest and most significant effort by the Justice Department to address the controversy. In earlier personnel changes, three ATF agents were laterally transferred starting in May from operational positions to administrative roles.