WASHINGTON (AP) — Senate Democrats and the White House struggled to break an impasse Thursday over Chuck Hagel's nomination as secretary of defense, with Republicans blocking speedy confirmation of their former colleague and Vietnam combat veteran.

Senate Majority Leader Harry Reid accused the GOP of filibustering Hagel's nomination, a move he described as unprecedented for a president's pick for defense secretary. Reid, D-Nev., needs only a few Republican votes to secure the 60 needed to clear Hagel's nomination for an up-or-down vote on the Senate floor.

But those remaining yes votes remain elusive. Republican senators, led by Lindsey Graham of South Carolina and John McCain of Arizona, vowed to delay the process unless they got more information about what President Barack Obama was doing on the night of the deadly attack on the U.S. diplomatic mission in Benghazi, Libya, where Ambassador Chris Stevens and three other Americans were killed. Their demand has the effect of a filibuster.

Seeking to break the logjam, the White House responded to a Feb. 12 letter from Graham, McCain and Sen. Kelly Ayotte, R-N.H. to Obama asking whether he spoke to any Libyan government official during the Sept. 11 assault about getting assistance. Republicans have sought to portray Obama as being out of touch during the raid.

Former Secretary of State Hillary Clinton called Libyan President Mohamed Magariaf on Obama's behalf on Sept. 11 to coordinate additional support to protect Americans in Libya, White House counsel Kathryn Ruemmler wrote in the Feb. 14 response. Obama spoke to Magariaf on the evening of Sept. 12, she said.

A White House official said there was no new information in Ruemmler's letter. The fact of Clinton's call to Magariaf has previously been public. If there were a need to push the Libyans to do something, Obama would have called, but the Libyans were trying to do the right thing and were being as helpful as possible, the official said.

The official, discussing internal communications only on the condition of anonymity, said that it wasn't clear that an earlier call from Obama to the Libyans would have been helpful in the deadly, fast-moving assault.

The offices of Graham, McCain and Ayotte did not immediately respond to a request for comment on Ruemmler's letter.

Reid said it was "shocking" and "tragic" that the GOP would attempt to block Hagel's nomination at a time when the U.S. military is engaged in so many places around the world. "Not a single nominee for secretary of defense ever in the history of our country has been filibustered," he said in a speech on the Senate floor.

Reid said Republicans notified him Wednesday night they would withhold the votes needed to advance Hagel's nomination. Reid said he considered that a "full-scale filibuster" because the Republican strategy would prevent Hagel's nomination from getting the required 60 votes.

Republicans are seeking "extraneous requests" for information that will never be satisfied, Reid said. "The pattern has been clear for months: as soon as President Obama's administration responds to one request, Republicans devise another, more outlandish request," Reid said.

A full Senate vote on Hagel, a former two-term Republican senator from Nebraska and twice-wounded Vietnam veteran, is expected to be held Friday after Reid filed a motion to limit debate. While Democrats hold a 55-45 edge in the Senate and have the numbers to confirm Hagel on a majority vote, they need the support of five Republicans to clear the way for a majority vote.

Two Republicans — Sens. Thad Cochran of Mississippi and Mike Johanns of Nebraska — have announced their support for Hagel. A third, Sen. Susan Collins of Maine, has said she will vote against Hagel's confirmation, but she would not join in a filibuster to block a final vote.

Graham said Wednesday that he would vote against ending debate on Hagel's nomination.

"There seems to not be much interest to hold this president accountable for a national security breakdown that led to the first ambassador being killed in the line of duty in over 30 years," Graham said. "No, the debate on Chuck Hagel is not over. It has not been serious. We don't have the information we need. And I'm going to fight the idea of jamming somebody through until we get answers about what the president did personally when it came to the Benghazi debacle."

McCain declined to say whether he would try to delay Hagel's confirmation if Obama did not provide an answer. "My position right now is I want an answer to the question," he said.

The nomination of John Brennan as CIA director is also being delayed; the Senate Intelligence Committee is pushing off a vote amid demands that the White House turn over more details about drone strikes against terror suspects and about the Benghazi attacks. Intelligence Committee Chairwoman Dianne Feinstein of California said a vote likely will be postponed till late February.

A bitterly divided Armed Services Committee on Tuesday voted to approve Hagel by a 14-11 vote, with all the panel's Democrats backing him. The committee's Republicans were unified in opposition to their onetime colleague, who will succeed Defense Secretary Leon Panetta if he's confirmed

Obama "stands strongly" behind Hagel and believes he "will do a wonderful job," White House spokesman Josh Earnest said aboard Air Force One en route to Decatur, Ga., where the president traveled Thursday to speak about early childhood education.

If confirmed by the Senate, Hagel, 66, would take charge of the U.S. armed forces at a time of turmoil. Automatic cuts to the Pentagon's budget are looming, American troops in Afghanistan are being halved over the next year, North Korea has tested a nuclear weapon, Iran remains a threat in the Persian Gulf region, and Syria, Iraq, Libya, Egypt, Mali and Tunisia all are in a state of unrest.

Reid said incorrectly that Panetta is departing his post Thursday, leaving the federal government's largest agency without a leader because Hagel has not been confirmed. But Panetta, who is retiring after 18 months in the job and will return to California, has committed to waiting until his successor is approved.

At a Pentagon award ceremony on Thursday for former Secretary of State Hillary Rodham Clinton, Panetta said it was fitting to recognize her accomplishments on Valentine's Day. And he said the second-best Valentine's Day present would be for the Senate to confirm Hagel and allow Panetta and his wife to "get the hell out of town." He said he's got his belongings packed.

Hagel has faced intense opposition from Republicans, who have challenged his past statements and votes on Israel, Iran, Iraq and nuclear weapons.

But the questions and comments before the Armed Services Committee vote on Tuesday took a more personal and confrontational turn. Sen. Ted Cruz, R-Texas, demanded that Hagel provide information on compensation for speeches over a five-year period — three years more than required — and suggested that without the information, the committee wouldn't know whether Hagel got money from "extreme and radical groups."

Reports about Iranian leaders praising Hagel's nomination back up Cruz's claim, said Sen. James Inhofe, the top Republican on the Senate Armed Services Committee. "I'd say he's endorsed by them. You can't get any cozier than that," Inhofe said.