WASHINGTON • United States Democratic presidential candidate Hillary Clinton has passed a tough political test, calmly deflecting harsh Republican criticism of her handling of the deadly 2012 attack in Benghazi, Libya, during a testy 11-hour hearing in Congress.

Mrs Clinton, 67, stayed out of the political fray during several heated arguments between Republicans and her Democratic allies and remained composed under the aggressive questioning from Republican lawmakers on Thursday.

In testimony that stretched deep into the night, the former secretary of state rejected Republican accusations that she misinformed the public about the cause of the suspected militant attack that killed four.

The hearing uncovered no new revelations in an incident that has been the subject of a half-dozen other probes. Mrs Clinton's long-awaited testimony was the most high- profile appearance yet before the panel. She said it was "personally painful" to be accused of ignoring security upgrades that could have saved the life of Ambassador J. Christopher Stevens and three other Americans. "I've thought more about what happened than all of you put together," she told the panel. "I've been racking my brain about what could have been done, should have been done."

The appearance was a critical hurdle for Mrs Clinton, who has been on a hot streak since her strong performance at the first Democratic debate and after news that Vice-President Joe Biden will not seek the Democratic election nomination.

Even some Republicans said Republican lawmakers had swung at Mrs Clinton and missed with their aggressive questioning.

"They forget Secretary Clinton has been dealing with hostile committees longer than most of them have been in politics at any level," Texas-based Republican strategist Joe Brettell said.

Mrs Clinton denied longstanding Republican allegations that she turned down requests to beef up security in Benghazi. "I was not responsible for specific requests and security provisions," she said.

She told the panel the attacks were thoroughly investigated. "We need leadership at home to match our leadership abroad, leadership that puts national security ahead of politics and ideology," she said, a veiled reference to the political controversy dogging the panel.

Democrat Elijah Cummings said congressional Republicans set up the panel for a partisan witch-hunt.

He called for an end to the "taxpayer-funded fishing expedition".

Panel chairman Trey Gowdy told Mrs Clinton: "I understand some people... have suggested this investigation is about you. Let me assure you it is not."

A Reuters/Ipsos poll this week found 35 per cent of US respondents viewed the hearings as mostly or completely valid.

REUTERS