(CNN) -- The Obama administration has responded to GOP questions about President Obama's actions on the night of the U.S. Consulate attack in Benghazi, administration officials said. Sen. Carl Levin, chairman of the Senate Armed Services Committee, received a letter from the White House, the sources said. This comes amid concern that Republicans will filibuster Obama's nomination of Chuck Hagel for defense secretary if they feel they aren't getting appropriate answers to their questions.