WASHINGTON -- Senate Republicans are following through on their threat to filibuster former Sen. Chuck Hagel (R-Neb.), President Barack Obama's nominee for defense secretary, Senate Majority Leader Harry Reid (D-Nev.) said Thursday morning.

"It is tragic that they have decided to filibuster this qualified nominee," said Reid. "It is really unfortunate."

The significance of Reid's announcement wasn't immediately clear, as he gave no indication as to whether or not Democrats had the 60 votes needed to overcome a Republican filibuster attempt. It was only after Reid finished speaking that a Democratic Senate aide confirmed that the majority leader doesn't yet have the votes to overcome a Hagel filibuster.

It was assumed that many Republicans would vote against Hagel but allow his nomination to come to an up-or-down vote. Reid said that blocking Hagel through procedural means would be unprecedented.

"This isn't high school getting ready for a football game, or some play being produced at a high school," said Reid. "In less than two hours, our country will be without a secretary of defense."

The first vote on Hagel's nomination will come on Friday. If Reid can muster 60 yes votes by then, the chamber will begin a debate period. After that, there will be a final vote on Saturday.

It is customary for a president to be granted the leeway to choose his own advisers. But Hagel was a controversial choice among his fellow Republicans, owing to his public criticisms of President George W. Bush's foreign policy, his advocacy for confronting Iran's nuclear program via diplomatic means and his past criticisms of the Israeli lobby's influence within the halls of Congress.

Speaking on the floor, however, Reid said that Republicans were holding up the nomination because of the administration's refusal to release additional information about the September attacks on the U.S. diplomatic outpost in Benghazi, Libya.

"Chuck Hagel had nothing to do with the attack in Benghazi," Reid said.

The last defense secretary who was not confirmed by the Senate was John Tower, whose admission of past personal transgressions led to his nomination's downfall by a vote of 53 to 47 in 1989. That was a defeat via regular order, not a filibuster.

UPDATE: 11:30 p.m. -- One of the issues holding up Hagel's nomination appears to be requests from Republicans in the Senate to receive specific intelligence about the Benghazi attack, intelligence that Reid insists has already been provided. In a statement issued after his floor speech, Reid said that the White House had sent Republicans a letter about the attack at 4:00 p.m. on Wednesday, the latest of a series of attempts by the administration to assuage their concerns about the incident.

That letter, however, was "not enough" for them, according to Reid.

They "are moving the goals posts at the last minute," he said. "This is no way to operate."

CNN's Dana Bash, however, spoke to Sen. John McCain (R-Ariz.) -- one of the senators who has most vocally demanded answers about Benghazi but who has also said he was against the idea of filibustering a cabinet nominee -– and got a different explanation. The letter, McCain said, was sent to Armed Services Committee Chair Carl Levin (D-Mich.), not Senate Republicans.

Hagel's own spokesman, meanwhile, acknowledged on Thursday that he could end up being rejected by the Senate.

“He could be defeated, but he’s not withdrawing," Aaron Dowd told National Journal. "It’s not something anyone is discussing."

UPDATE: 11:50 p.m. -- The White House has now weighed in.

"We urge the Republicans in the Senate to drop their delay," said spokesman Josh Earnest, briefing reporters en route to the president's speech in Georgia. "There is a clear majority in the United States Senate for Senator Hagel's confirmation. These delaying tactics are unconscionable, and they should end right away."

Meanwhile, an official working to help Hagel get confirmed offers the following whip count:

We have 55 Dems and Independents on board for cloture, plus Senators Johanns and Cochran (the Republicans who’ve announced they’re voting for Hagel’s nomination). Add onto that Susan Collins saying she will vote for cloture yesterday, and we need two more votes to get to 60. That’s the state of play right now.

UPDATE: 1:15 p.m. -- Sen. Lindsey Graham (R-S.C.) and Sen. Lamar Alexander (R-Tenn.) have reportedly said they will also vote for cloture -- but only after the President's Day recess, which lasts through the end of next week.

Sam Stein's wife works for the Obama administration on matters of congressional oversight.

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  • Chuck Hagel (February 2013 - Present)

    New Secretary of Defense Chuck Hagel is greeted as he arrives for his first day at the Department of Defense, on February 27, 2013 in Arlington, Va. (Photo by Drew Angerer/Getty Images)

  • Leon Panetta (July 2011 - February 2013)

    Secretary of Defense Leon E. Panetta pauses while speaking during a ceremonial swearing-in at the Department of Defense July 22, 2011 in Washington. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Robert Gates (Dec. 2006 - July 2011)

    Robert Gates speaks during his ceremonial swearing in as the 22nd defense secretary on Dec. 18, 2006 at the Pentagon. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Donald Rumsfeld (Jan. 2001 - Dec. 2006)

    U.S. Secretary of Defense Donald Rumsfeld holds his press conference at the Pentagon briefing room on Jan. 26, 2001 in Arlington, Va. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • William Cohen (Jan. 1997 - Jan. 2001)

    Secretary of Defense designate William Cohen testifies during confirmation hearings before the Senate Armed Services Committee on Jan. 22, 1997 in Washington. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • William Perry (Feb. 1994 - Jan. 1997)

    U.S. Defense Secretary William Perry points to a reporter during a press conference on April 21, 1994 in Seoul, Korea. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Les Aspin (Jan. 1993 - Feb. 1994)

    U.S. Secretary of Defense Les Aspin released new regulations governing gays in the military during a press on Dec. 22, 1993 at the Pentagon. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Dick Cheney (March 1989 - Jan. 1993)

    U.S. Defense Secretary Dick Cheney (L) meets Egypt's President Hosni Mubarak, on April 3, 1989, at Washington. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Frank Carlucci (Nov. 1987 - Jan. 1989)

    U.S. Defense Secretary Frank Carlucci testifies before the Senate Armed Services Committee on July 13, 1988 in Washington. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Caspar Weinberger (Jan. 1981 - Nov. 1987)

    Caspar Weinberger, Secretary of Defense on Feb. 9, 1981. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Harold Brown (Jan. 1977 - Jan. 1981)

    General Alexander M. Haig, right, retired as NATO commander, walks with Defense Secretary Harold Brown during an awards ceremony on July 3, 1979 at Fort Myer, Va. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Donald Rumsfeld (Nov. 1975 - Jan. 1977)

    A 1976 photo of Secretary of Defense Donald Rumsfeld. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • James Schlesinger (July 1973 - Nov. 1975)

    Israeli Defense Minister Moshe Dayan, left, with Secretary of Defense James R. Schlesinger, chats on Friday, Jan. 5, 1974 at the Pentagon. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Elliot Richardson (Jan. 1973 - May 1973)

    Elliot L. Richardson speaks to newsmen Oct. 23, 1973 at a press conference held at the Department of Justice. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Melvin Laird (Jan. 1969 - Jan. 1973)

    Secretary of Defense Melvin R. Laird as he departed from Andrews Air Force Base Md., for Paris on Jan. 5, 1971 in Washington. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Clark Clifford (March 1968 - Jan. 1969)

    This is an Oct. 1968 photo of Secretary of Defense Clark Clifford as he announces his support for President Johnson's decision to halt the bombing of North Vietnam. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Robert McNamara (Jan. 1961 - Feb. 1968)

    PARIS, FRANCE: US Secretary of Defense Robert McNamara smiles as he arrives 27 November 1965 at Paris' NATO headquarters. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Thomas Gates (Dec. 1959 - Jan. 1961)

    Secretary of Defense Thomas S. Gates Jr., center, poses with Benjamin M. McKelway, left, editor of the Washington Evening Star and President of the AP, and AP General Manager Frank J. Starzel at the April 25, 1960 meeting of the Associated Press in New York. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Neil McElroy (Oct. 1957 - Dec. 1959)

    Defense Secretary Neil McElroy said he has "fullest confidence that the United States is ahead of the Soviets..." prior to the announcement of the Soviet's achievement in launching the first earth satellite, Oct. 4, 1958. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Charles Wilson (Jan. 1953 - Oct. 1957)

    Charles E. Wilson, left, takes the oath of office from Chief Justice Fred Vinson at the White House in Washington on Dec. 21, 1950 as head of the office of Defense Mobilization. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Robert Lovett (Sept. 1951 - Jan. 1953)

    Gen. Dwight D. Eisenhower (right) watches President Harry S. Truman and Gen. Omar Bradley help Defense Secretary Robert Lovett (left) get in place as the men posed on the south lawn of the White House on June 1, 1952 in Washington. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • George Marshall (Sept. 1950 - Sept. 1951)

    Anna M. Rosenberg, New York Labor and Public Relations consultant, who is named assistant secretary of defense, chats with Secretary of Defense George Marshall in a conference at the Pentagon on Nov. 9, 1950 in Arlington, Va. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • Louis Johnson (March 1949 - Sept. 1950)

    Defense Secretary Louis Johnson (right) gives new identification card to President Harry Truman at the White House on Nov. 9, 1949 in Washington, listing him as commander in chief for an "indefinite" term. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)

  • James Forrestal (Sept. 1947 - March 1949)

    James V. Forrestal, Secretary of Defense under President Harry Truman, is shown on July 26, 1947. (Source: <a href="http://www.defense.gov/specials/secdef_histories/">Department of Defense</a>)