Former Secretary of State Hillary Clinton called the Sept. 11, 2012, attacks on U.S. facilities in Benghazi, Libya, that left four Americans dead the “biggest regret” of her diplomatic career.

“My biggest regret is what happened in Benghazi,” she said during a question-and-answer session that tailed her keynote address at the National Automobile Dealers Association convention on Monday, The Washington Post reported.

Among the four Americans killed in the terrorist attack was Ambassador J. Christopher Stevens. The Obama administration for days after the attack played down the label of terrorism and put forth the formal line instead that the killings arose from an impromptu gathering of militants who were angered by what was perceived as an American-created, anti-Islamic video that made the YouTube rounds.

Mrs. Clinton later made national headlines when she famously addressed a Senate query about her role in the attacks with a heated response: “With all due respect, the fact is we had four dead Americans. Was it because of a protest or was it because of guys out for a walk one night decided to go kill some Americans? What difference at this point does it make?”