A Republican lawmaker threatened Sunday to block the confirmations of President Barack Obama's nominees for defense secretary and CIA director over the deadly attack on the US consulate in Libya.

Senator Lindsay Graham said he would put a "hold" on the nominations of Chuck Hagel and John Brennan until the White House provided more information about the president's actions during the September 11, 2012 attack in Benghazi, Libya.

"I want to know what our president did. What did he do as commander in chief? Did he ever pick up the phone and call anybody? I think this is the stuff the country needs to know," Graham said on CBS' Face the Nation.

The US Senate has held hearings on the nominations of Hagel as defense secretary and Brennan as CIA director, but has yet to confirm them.

Under parliamentary rules, a single senator can stop their nomination from coming to a vote of the full Senate.

"I don't think we should allow Brennan to go forward to the CIA directorship, (or) Hagel to be confirmed for secretary of defense, until the White House gives us an accounting," Graham said.

Senator Jack Reed, a Democrat, said it was "unprecedented, unwarranted" to block a vote on the defense secretary nomination.

"The men and women of the Department of Defense need a secretary of defense," he said on the same CBS talk show.

"These are critical offices," he said. "To dwell on a tragic incident and use that to block people is not appropriate."

Four Americans were killed in the attack, including US ambassador to Libya Chris Stevens.

Graham and other Republicans have accused the administration of misleading the public by initially blaming it on a mob inflamed by an anti-Muslim video, rather than a terrorist attack.

Susan Rice, the US ambassador to the United Nations, withdrew from consideration for secretary of state amid controversy over her account of the attack.

On Sunday, Graham turned the focus on Obama, questioning whether he made any phone calls to Libyan leaders during the crisis to try to clear the way for a rescue team that had been sent from Tripoli to Benghazi as reinforcements after the attack.

"This was incredibly mismanaged. And what we know now, it seems to be a very disengaged president," he said.