Hillary Clinton has told a Congressional committee that she took responsibility after the 2012 attack on US consulate in Benghazi, Libya, that killed Ambassador Chris Stevens and three other Americans.
The Democratic presidential hopeful added that as secretary of state she introduced reforms to protect diplomatic staff after the attack.
Committee chairman Trey Gowdy said: “We owe them [the victims] the truth.”
Hillary Clinton’s party says the Republican-led panel is a witch-hunt trying to harm her presidential bid.
In her opening statement at the congressional hearing, Hillary Clinton said she had asked Chris Stevens to go to Libya as US ambassador.
“After the attacks I stood next to President Obama as Marines carried his casket,” she said.
Hillary Clinton said her appearance was her way of honoring the lives lost, and she called on those present to put national security above partisan politics.
Democratic Representative Elijah Cummings, seated next to the chairman, said Republicans were wasting taxpayer money in an effort to derail Hillary Clinton’s presidential campaign.
However, Trey Gowdy denied his committee was going after Hillary Clinton.
Instead, he said, it was looking for the truth behind the diplomatic compound’s unsuccessful requests for more security and personnel in the build up to the attacks.
There have already been seven congressional investigations into the attack, by suspected Islamist militants, on the US compound in the Libyan city of Benghazi on September 11, 2012.
The raid led to the deaths of Ambassador Chris Stevens and three other US embassy staff.
Hillary Clinton said Chris Stevens was well aware of the risks of his job but withdrawing American presence from Libya would have been a mistake.
“To retreat from the world is not an option. America cannot shrink from our ability to lead,” she said.
When the US pulls out of places, extremists gain a foothold, Hillary Clinton added, although she did admit that security requests made by the Benghazi consulate were not met.
An independent review board found deficiencies within the State Department that the Obama administration has tried to fix, Hillary Clinton said.
Observers say this is a key moment for Hillary Clinton, who solidified her position as the Democrats’ frontrunner for presidential candidate after her potential rival, VP Joe Biden, ruled himself out of the race on October 22.
Hillary Clinton’s appearance before the House of Representatives Select Committee on Benghazi could further strengthen her position or raise doubts about her suitability as a presidential nominee.