Hillary Clinton on Benghazi: 'Arab Spring shattered security in region' Nobody is more committed to getting this right. I am determined to leave the State Department and our country safer, stronger and more secure," she added. Carry teams move flag draped transfer cases of the remains of the four Americans killed in Benghazi (AP) She warned the committee, however, that US diplomacy could not pull back in face of the new challenges posed by the evolving geopolitical landscape, saying the United States had to meet a "changing threat environment." We cannot afford to retreat now. When America is absent, especially from unstable environments, there are consequences. Extremism takes root, our interests suffer, and our security at home is threatened," she said. French soldiers patrol in the recently liberated town of Diabaly, Mali (EPA) Mrs Clinton also highlighted "instability in Mali," saying it "has created an expanding safe haven for terrorists who look to extend their influence and plot further attacks of the kind we saw just last week in Algeria." The secretary of state also dismissed charges that the US had sought to cover-up events surrounding Benghazi. I just want to say that people have accused ambassador (Susan) Rice and the administration of misleading Americans. I can say, trying to be in the middle of this and understanding what was going on, nothing could be further from the truth," Mrs Clinton said. What difference does it make. Despite keeping a low profile after a long period of ill health in her final weeks in office, Mrs Clinton is keen to draw a line under the deadly September 11 Benghazi assault, which triggered a political storm in the US. The hearings have also taken on added urgency as Washington reels from an attack on a remote Algerian gas plant in which three Americans were killed. The two events graphically illustrate warnings already highlighted by Mrs Clinton about the dangers posed by extremists - and in particular al-Qaeda in the Islamic Maghreb - to US and Western interests in North Africa. Mrs Clinton was initially due to testify in December after a scathing inquiry blamed "grossly inadequate" security at the outpost in Benghazi, eastern Libya, for failing to protect staff there. But she was forced to send in her two deputy secretaries instead when she fell ill with a stomach bug, and later suffered a concussion in a fall, and a blood clot. Her testimony to two congressional committees comes on the eve of a Senate hearing to confirm her successor, Senator John Kerry, who is expected to be easily voted in and could take over within days as the top US diplomat. Mrs Clinton is stepping down from office with approval ratings hovering around 65 per cent, and already there is a growing clamour among supporters for her to run for president in 2016. But the Benghazi assault, in which Ambassador Chris Stevens and three other Americans died, as well as her month-long absence, have marred her final weeks. Since returning to work in early January, Mrs Clinton, 65, has met only a handful of foreign dignitaries at the State Department, and has held few events open to the press. She been unable to get back on a plane for another whistle-stop tour to some far-flung part of the world, having been effectively grounded after notching up a record-breaking 112 countries. Wednesday's appearances at the Senate Foreign Relations committee at 9:00am (1400 GMT), followed in the afternoon by the House Foreign Affairs committee, will finally give Senators the chance to grill her about Benghazi. "It's been a cover-up from the beginning," Republican Senator John McCain said on Tuesday, adding that he wanted to press Mrs Clinton on where she was on that night, and what warnings there had been about deteriorating security. Conservative Republican congressman Jeff Duncan anticipated asking "some very pointed questions" in the House hearing. America has a lot of questions. What exactly was going on at the so-called consulate in Benghazi? It was a special mission, OK? It was a special mission. What was its mission?" he asked. And if we're spending money all around the world, giving money away to a lot of countries that don't like us very much, why aren't we spending money to guard the Americans that put their lives on the line? All lingering questions would be answered, State Department spokeswoman Victoria Nuland pledged. "Tomorrow, both on the Senate side and on the House side, members of Congress will have a chance to hear what the secretary has to say, but also to ask her any remaining questions that they have on this matter," she said. Mrs Clinton is also expected to outline the steps taken to meet all 29 recommendations made by an Accountability Review Board she appointed to investigate the attack. She will "want to make clear the implementation that is set in train, the lessons that we are learning, but that implementation needs to be seen all the way through by her successor," Ms Nuland added.