Pressure had been building on ambassador Susan Rice after she admitted releasing incorrect information following the September 11 attack on the American consulate in Libya.
The attack left four Americans dead, including the Ambassador to Libya, Christopher Stevens.
Rice initially said the attack had followed protests over an anti-Islamic film, but later intelligence reports suggested a possible al-Qaeda connection.
Rice, the US Ambassador to the UN, admitted her mistake in late November, but several Republican senators said questions remained unanswered.
After Rice pulled out of the running to become Secretary of State today, Republicans vowed to continue "seeking the facts" about Benghazi.