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Sen. Lindsey Graham vowed Friday to hold President Obama "accountable" for his leadership on Benghazi, after the top two Defense Department leaders testified that they had just one conversation with Obama during the course of the Sept. 11 terror attack.

During testimony before the Senate Armed Services Committee Thursday, Defense Secretary Leon Panetta and Joint Chiefs Chairman Gen. Martin Dempsey said they spoke with Obama at 5 p.m. ET on Sept. 11 last year. They were both on the same call, and said it lasted about 30 minutes.

Dempsey said they did not speak again until the attack was over.

Graham, who had demanded that Panetta testify on Libya as a condition for allowing the nomination of Chuck Hagel to proceed, aggressively questioned both witnesses on the president's actions.

Graham wrote on his Twitter account Friday: "President Obama has to account for his leadership on #Benghazi and I intend it hold him accountable."

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He said Thursday on Fox News that "thus far the White House has delayed, denied, deceived and stonewalled and this has to come to an end. He has to account for his leadership."

During the hearing, Graham questioned why there weren't subsequent follow-up conversations with the president.

"It lasted almost eight hours ... did the president show any curiosity?" Graham asked.

Panetta said there was "no question" Obama "was concerned about American lives."

"With all due respect," Graham responded, "I don't believe that's a credible statement if he never called and asked you, 'are we helping these people?'"

Panetta, as well as committee Chairman Sen. Carl Levin, D-Mich., defended the president, noting that he has advisers around him to keep him abreast of breaking developments.

"The president is well-informed about what is going on -- make no mistake about it," Panetta said. He said he assumed the chief of staff was talking to Obama about the developments.

A senior defense official also said Friday that after the initial meeting, senior Defense and Joint Staff officials participated in a secure video teleconference with other White House officials, as well as officials from the State Department and CIA. The official said communication between the White House and Pentagon continued through the night.

During the hearing, Graham asked both Panetta and Graham whether they went to sleep that night. They said they did not -- they could not say whether the president did.

"Do you, either one of you, understand some of the frustrations we have?" Graham asked. "This is the first time in 30 years we lost control of an ambassador, and no small deal."

Ambassador Chris Stevens was killed, along with three other Americans, in the attack.

Panetta and Dempsey claimed Thursday that the military could not have done more to save American lives that night, claiming that the difficulty in dispatching assets to the scene was "a problem of distance and time."

Further, they suggested armed aircraft like F16s could have done more harm than good in a chaotic situation.

"There was not enough time given the speed of the attack for armed military assets to respond," Panetta said before the Senate Armed Services Committee. "We were not dealing with a prolonged or continuous assault which could have been brought to an end by a U.S. military response. ... Time, distance, the lack of an adequate warning, events that moved very quickly on the ground prevented a more immediate response."

Still, he said the Pentagon "spared no effort ... to save American lives."

Panetta testified in what was likely his final public appearance on Capitol Hill as he prepares to leave the department. His testimony followed that of Secretary of State Hillary Clinton last month.