The former US Secretary of State and Democratic presidential candidate Hillary Clinton is testifying before a committee investigating the 2012 attack on the American diplomatic compound in Benghazi in Libya.
Four US citizens including the US ambassador to Libya were killed in the attack.
The US compound in Benghazi was attacked on the night of 11 September, 2012.
US Ambassador Chris Stephens was there with fewer security personnel than he had when he first arrived in 2011. During the attack the ambassador and three others were killed.
Ms Clinton was Secretary of State at the time and has been quizzed over why security levels were so low in a conflict zone on the anniversary of 9/11.
She has previously testified before the House Foreign Affairs Committee and today is before the House Select Committee.
Democrats have accused Republicans of setting up the committee to tarnish Ms Clinton ahead of the 2016 election, something House Majority Leader Kevin McCarthy alluded to in a recent interview.
However, the committee chairman, Republican Trey Gowdy, said it is simply seeking answers as to why security was not ramped up following a request from the ambassador.
The hearing is expected to last about eight hours.
Meanwhile, Ms Clinton extended her lead in polls over fellow White House hopeful Bernie Sanders in the 2016 Democratic nomination race, while her leading Republican rival Donald Trump has done the same.
Ms Clinton impressed in her party's first televised debate last week in Las Vegas, while Mr Trump keeps rising as the tycoon taps into nationwide anti-Washington sentiment.
