U.S. Ambassador to Libya Chris Stevens and three members of his staff died when militants attacked the U.S. consulate office in Benghazi, Libya, in September. The U.S. government categorized the attack as an act of terrorism.
Republican leaders have been critical of President Obama's handling of the attack, accusing the administration of misleading lawmakers about the incident. U.S. Secretary of State John Kerry was asked by lawmakers early this year about the security in place at the consulate. Former Secretary of State Hillary Clinton was at times abrasive during similar questioning.
Former State Department spokeswoman Victoria Nuland faced tough questions on Benghazi during testimony Thursday before the Senate Foreign Relations Committee. She's been nominated to serve as assistant secretary of state for European and Eurasian affairs.
Sen. John Barrasso, R-Wyo., was quoted by The Wall Street Journal as saying he doubted Nuland's credibility because she "intentionally withheld information about Benghazi."
Nuland defended her role at the State Department, saying she was a press liaison, not a policymaker.
"I am 400 percent committed to positive cooperation with the Congress," she said.
Republican lawmakers have made their frustration with Obama known by delaying key administrative appointments.
The FBI in May said it was looking for information about three men seen on the grounds of the U.S. consulate in Benghazi at the time of a deadly September attack. It published images on its website of the alleged suspects.