US Secretary of State Hillary Clinton vowed Wednesday to answer lingering questions about last month's deadly attack on a US mission in Libya, seeking to counter a barrage of Republican criticism.

"There are continuing questions about what exactly happened in Benghazi on that night three weeks ago and we will not rest until we answer those questions and until we track down the terrorists who killed our people," Clinton said.

"The men and women who serve this country as diplomats deserve no less than a full and accurate accounting, wherever that leads."

But the top US diplomat warned against snap judgments, despite a growing clamor for information about the September 11 attack on the US mission in Benghazi in which the US ambassador, Chris Stevens, was killed with three other Americans.

"Let's establish all the facts before we jump to any conclusions, and let's do so so that we can get to the bottom of what did happen," Clinton said.

Four weeks before the November 6 elections, the attack is a dominant theme of the campaign, as Republican opponents seek to make political capital out of it, alleging there were serious security lapses.

Republican Representative Darrell Issa, chairman of the House Oversight and Government Reform Committee, has called a hearing on October 10 to probe the events in Benghazi, and urged Clinton to provide answers.

Republicans have lashed Obama over the attack, raising questions about the administration's security and foreign policies, and suggesting there has been a cover-up into security failures.

Initially, the Obama administration insisted the Benghazi assault was a spontaneous protest against an anti-Islam film, which had sparked demonstrations the same day in Cairo when the US embassy was stormed.

But late last week, it finally acknowledged that Al-Qaeda elements may have been linked to the attack in which the Benghazi compound was gutted by fire.

US military and intelligence services have mobilized to figure out exactly who carried out the attack and to launch operations to capture or kill the militants, a US defense official told AFP.

The official confirmed the manhunt was a top "priority" and would be carried out in cooperation with intelligence agencies and the Libyan government.

Meanwhile, The Washington Post reported that it had gained access to the ruined compound, which is supposed to be guarded by local Libyan security staff, and found sensitive documents scattered about the rooms.

The documents included information on a weapons collection scheme, personnel records of local Libyan staff, and Stevens's travel plans for the week.

Last week, CNN reported it had found Stevens's diary in the gutted building in which he alleged he had been on an Al-Qaeda hit list, redoubling the questions about whether he was given proper security.

Clinton urged there should be a "rigorous, careful" investigation, but did not answer a question about allegations that requests for extra security in Libya had been denied.

She has set up an inquiry into whether security measures at the consulate were properly implemented, headed by veteran diplomat Thomas Pickering, and including Admiral Mike Mullen, former chairman of the Joint Chiefs of Staff.

"I am aware too that many people are eager for answers. So am I. And no one wants the answers more than we do here at the department," Clinton said after talks with Kazakh Foreign Minister Yerlan Idrisov.

She added that she has asked the review to move "as quickly as possible without sacrificing accuracy. In the interim, we will provide as much accurate information to the Congress and the public along the way."

In his letter to Clinton, Issa detailed a dozen attacks or threats against US and Western staff in Benghazi in the months before the attack -- including two bomb attacks on the consulate.