WASHINGTON -- Three Republican senators on Wednesday demanded the creation of a special panel to investigate the September attacks on the U.S. consulate in Benghazi, Libya, that killed U.S. Ambassador Christopher Stevens and three other Americans.

Sen. John McCain, R-Ariz,. joined Sens. Lindsey Graham, R-S.C., and Kelly Ayotte, R-N.H., in saying the standard congressional committees aren’t up to the task of unraveling the complex series of diplomatic, military and intelligence missteps tied to the tragedy in Benghazi.

“While we await the findings and recommendations of the (Obama) administration’s internal review, it’s essential for the Congress to conduct its own independent assessment,” McCain said at a news conference. “There is no credibility amongst most of us considering the administration and the numerous controversies and contradictions that have been involved in their handling of this issue.”

Obama said his administration is working with Congress and conducting its own "full-blown investigation" into the consulate assault in Benghazi, which came on the 11th anniversary of the Sept. 11, 2001, terrorist attacks.

“It is important for us to find out exactly what happened in Benghazi, and I’m happy to cooperate in any way Congress wants,” Obama said at his first post-election news conference. “We have provided every bit of information that we have, and we will continue to provide information.”

Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate Intelligence Committee, rejected the need for a special panel and said her committee is adequate to probe the security lapses before and during the nighttime military-style raids on the consulate.

“We have spent a great deal of time on this,” Feinstein told reporters. “We have arranged for three hearings on the intelligence aspects. We’re the committee that should do it, we’re the committee with responsibility for oversight and that has the authority to do it.”

Feinstein said that former CIA head David Petraeus, who resigned the post last week because of an extramarital affair, had agreed to testify to her panel about the Benghazi attacks.

House Speaker John Boehner, R-Ohio, said he didn’t think a special committee is necessary.

“At this point, I think that the standing committees of the House, whether they be the (State Department) oversight committee or the intelligence committee, are working diligently on these issues,” Boehner said.

Graham said that at least two other Senate panels – the Foreign Relations Committee and the Armed Services Committee, on which he sits – would also investigate the attacks.

“Four Americans are dead, the first (U.S.) ambassador is killed in 33 years in the line of duty,” Graham said. “I think this is a symptom of a greater problem in the Middle East, quite frankly.”

The U.S. consulate in Benghazi was based at a group of villas. A separate cluster of U.S.-leased villas just over a mile from the consulate housed a secret CIA mission, which came under sustained mortar attack hours after the initial hit on the consulate.

Graham and the senators cited previous select committees Congress set up to probe the Sept. 11, 2001, attacks, the Watergate scandal and the Iran-Contra affair as models for a unified probe of the Benghazi attacks.

“Conspiracy theories are running rampant” about Benghazi, Graham said. “A segmented, stovepipe investigation, where you have three different committees going off in three different directions, not comparing notes, not being able to do this in an organized fashion, is going to lead to failure.”

The separate congressional hearings, Graham said, would be unlikely “to hold people accountable for what I think is a national security debacle long in the making that should have been avoided.”

Sen. Claire McCaskill, D-Mo., who often works with Republicans, said she isn’t convinced a select committee is needed.

“Classified briefings are very important, and we should let those run their course,” McCaskill told McClatchy. “It would appear to me we have aggressive oversight going on right now, and that’s what we should continue to do.”

It is unusual for Congress and a presidential administration to agree to the creation of a special committee to probe a major national security lapse.

Even after the Sept. 11, 2001, attacks that killed almost 3,000 Americans, President George W. Bush and some Republican allies in Congress resisted for months establishing a panel to investigate.

The 9/11 panel wasn’t created until 14 months later. After 20 months of work, including interviews with 1,200 people in 10 countries and a review of several million documents, it released a report that blamed multiple random and systemic intelligence lapses for the tragedy.

Michael Doyle and Lindsay Wise of the Washington Bureau contributed.