My biggest regret is what happened in Benghazi: Hillary Clinton

Gearing up for a possible 2016 presidential run, former United States Secretary of State Hillary Clinton has said the "biggest regret" of her tenure was the 2012 attack on a US consulate in Libya that killed four Americans, including its ambassador.

"You know, my biggest regret is what happened in Benghazi. And it illustrated one of the biggest problems that I faced as secretary of state," Clinton said in her keynote address before the National Automobile Dealers Association in New Orleans.

"We have a lot of dangerous locations where we send not our military, but our civilians. And they go in, they have language skills, often. They try to assess what's going on in the area.But they are vulnerable," she said.

Four US nationals, including the US Ambassador to Libya Chris Stevens, were killed in a terrorist attack at US Consulate in Benghazi in 2012.

"We had a very small outpost there, the Central Intelligence Agency had a very big well-defenced one. Two of our people died at the outpost. Two died on the roof of the CIA annex. So, you know, it's a constant balancing. And I had to do that all of the time, and obviously it was a great personal loss to me since I sent Stevens to Libya the first time," she said.

The attack became a political flashpoint in the run-up to the 2012 election, with Republicans arguing that President Barack Obama tried to play down its significance as he campaigned for a second term. Republicans might make it an issue if Clinton runs for the president's office in 2016.

Clinton has not made it clear yet if she would run for the post of the president in 2016.