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The acting director of the ATF, Kenneth Melson, and the U.S. attorney for Arizona, Dennis Burke, are resigning over the controversial gun-running investigation known as Fast and Furious.

Melson announced the moves in a Tuesday morning conference call. Burke released a statement shortly after.

The ATF acting director will become a senior advisor in the Department of Justice. Burke has delivered a letter of resignation to the president, his office said.

The moves follow a call by Republicans for an investigation into the ATF probe.

"While the reckless disregard for safety that took place in Operation Fast and Furious certainly merits changes within the Department of Justice, the Oversight and Government Reform Committee will continue its investigation to ensure that blame isn’t offloaded on just a few individuals for a matter that involved much higher levels," said Rep. Darrell Issa, R-Calif., in a press release.

Burke's resignation, which is effective immediately, comes just days after he testified before Issa's committee. The Fast and Furious operation has become a political scandal after many weapons tracked by the ATF were smuggled into Mexico. Weapons purchased by straw buyers in transactions known to the ATF were found at the scene of a Rio Rico firefight that killed Border Patrol Agent Brian Terry last December.

ATF officials have testified that the operation was aimed at taking down large-scale gun trafficking networks. Agents watched illegal gun sales, sometimes with the cooperation of firearms dealers, and tracked the movement of the weapons. In many cases, the agency lost track of the guns.

"My long tenure in public service has been intensely gratifying. It has also been intensely demanding. For me, it is the right time to move on to pursue other aspects of my career and my life and allow the office to move ahead," Burke said in an email to his staff.

Burke did not reference the Fast and Furious investigation in his statement.

In other moves related to Fast and Furious, Assistant U.S. Attorney Emory Hurley, was reassigned from the criminal to the civil division. Emory, based in Phoenix, had direct oversight of the gun-smuggling probe. Also in Phoenix, three of the four whistleblowers on the case have been reassigned to new positions outside the state.

Ann Scheel, an assistant U.S. attorney, will act in Burke's place until a replacement is appointed.

Burke has served as the U.S. attorney for the state since September 2009. He is a former advisor to Homeland Security Secretary Janet Napolitano, and served as her chief of staff when she was governor. Prior to that, Burke worked in the state attorney general's office.

U.S. Attorney General Eric Holder praised Burke's work in a statement.

"Under his leadership, the office has made great progress in its pursuit of justice with the creation of special units focusing on civil rights enforcement and rule of law, as well as more robust outreach to key communities, particularly in Indian Country," Holder said. "The office’s quick response to the devastating shootings in January that claimed the lives of several people and critically injured Congresswoman Gabrielle Giffords was crucial in arresting and charging the alleged shooter."

Republican Sen. John McCain issued a terse statement on Burke's resignation: "I thank Dennis Burke for his many years of dedicated public service to the people of Arizona and our nation, and wish him all the best in his future endeavors."

B. Todd Jones, the top federal prosecutor in Minnesota, will become acting head of the ATF as he continues to serve as U.S. Attorney. The Senate has not confirmed an ATF director for years, because of objections by gun-rights groups. Melson had led the agency since 2009.

Melson's move to a different position in DOJ drew criticism from Sen John Cornyn, R-Tex.

"Instead of reassigning those responsible for Fast and Furious within the Department of Justice," Cornyn said, "Atty. Gen. Holder should ask for their resignations and come clean on all alleged gun-walking operations, including a detailed response to allegations of a Texas-based scheme.

Troubled work history for Az's U.S. Attorneys

Burke's resignation makes him the second of Arizona's last three chief federal prosecutors to leave office unexpectedly.

Paul Charlton, the first U.S. Attorney for Arizona appointed by President George W. Bush, was forced out in late 2006 because of clashes with Attorney General Alberto Gonzales over the death penalty and the investigation into a land swap involving Rep. Rick Renzi.

Charlton was one of seven U.S. Attorneys fired by the Bush administration in a purge.

His successor, Dian Humetewa, resigned as expected in 2009 to clear the way for the Obama administration to appoint Burke.

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