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J. Scott Applewhite, Associated Press
Rep. Jason Chaffetz, R-Utah, left, speaks with Rep. Paul Gosar, R-Ariz., right, during a break at a House Oversight Committee hearing investigating last year's deadly assault on the U.S. diplomatic mission in Benghazi, Libya, on Capitol Hill in Washington, Wednesday, May 8, 2013.

SALT LAKE CITY — Rep. Jason Chaffetz joined other GOP lawmakers Wednesday to demand more cooperation from the White House with Congress' investigation into last year's deadly attack on the U.S. diplomatic post in Benghazi, Libya.

"This is not going to go away until the White House comes clean. And they haven't," Chaffetz told the Deseret News after a press conference in Washington, D.C., featuring six Republican members of the House and Senate.

Chaffetz, a member of the House Oversight Committee that has held hearings on the Sept. 11, 2012, attack, said the administration is withholding information and has not allowed any of the survivors to testify in public.

Until that changes, South Carolina Sen. Lindsey Graham pledged to block President Barack Obama's nominees from being confirmed in the Senate, including for Federal Reserve chairman and Homeland Security secretary.

Graham dismissed concerns expressed by the administration that the survivors could be called as witnesses in a terrorism prosecution and congressional testimony could jeopardize the case.

The South Carolina senator said Congress must be able to perform its oversight role into an attack that left four Americans dead, including U.S. Ambassador Chris Stevens.

Holding up the president's nominations is a way to "tell the administration, 'For the good of the country and for future oversight purposes, you cannot hide behind a criminal investigation,'" Graham said.

"This takes it to another level," Chaffetz said. He said Graham and Sen. John McCain, R-Ariz. — who is asking for a bipartisan House and Senate select committee on Benghazi — "have the political oomph to make things happen."

Chaffetz said the investigation has been slowed by what he described as stonewalling by the administration. The single witness to the attack who did testify, he said, did so in a closed hearing only after being subpoenaed.

"Nobody's been brought to justice. Nobody's been held accountable. Nobody's been fired," Chaffetz said, adding that the incident exposes vulnerabilities at other embassies and consulates around the world.

Congress, he said, wants to know why the Benghazi post was not better protected, why the military did not immediately respond and why the administration initially blamed the attack on a demonstration over an offensive film.

Both Graham and McCain alleged that the Democratic president sought to deceive voters before last November's election. GOP presidential candidate Mitt Romney was criticized for trying to take political advantage of the tragedy.

Chaffetz said the press conference was held because of a "60 Minutes" story broadcast Sunday that described a well-planned attack by al-Qaida against an American outpost that had minimal protection.

He said only Republicans participated in the press conference because "Democrats have circled their wagons around President Obama. It mystifies me why they are not concerned."

The administration has already made "extraordinary efforts to work" with Congress, White House spokesman Jay Carney said earlier this week, according to The Associated Press.

Carney said the administration has provided testimony at 13 hearings, participated in 40 staff briefings and turned over 25,000 pages of documents.

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