Kerry Vows 'to Leave No Stone Unturned' on Benghazi

U.S. Secretary of State John Kerry on Thursday vowed to "leave no stone unturned" to find out what happened during an attack on a U.S. mission in Libya last year in which four diplomatic staff were killed.

But he refused to wade into the issue more fully during a trip to Rome, after U.S. diplomats testified on Wednesday that the State Department could have done more to safeguard the Benghazi diplomatic outpost.

Pleading that on his whirlwind overseas tour he had only seen "the most cursory headlines", Kerry said he was "really not in a position to start making judgments" about the revelations at a congressional hearing.

"The State Department will leave no stone unturned," Kerry vowed though, adding his chief of staff, David Wade, was responsible for liaising with U.S. lawmakers on the attack.

Ambassador Chris Stevens and three other Americans were killed in the September 11 assault, when hordes of heavily-armed militants stormed the compound and a nearby annex.

Gregory Hicks, the deputy head of the mission and the first U.S. official who was on the ground to speak publicly about what happened, testified that he and many others knew from the start that it was a deliberate act of terror.

He told Wednesday's hearing of the House Oversight and Government Committee that he was shocked when the U.S. administration publicly argued otherwise.

The testimony by "whistleblowers," as the committee's Republican chairman Darrell Issa called them, is the latest in a months-long series of hearings to put the attacks and the U.S. response under a microscope.

The attack happened during the tenure of Kerry's predecessor, Hillary Clinton, but the new chief U.S. diplomat said: "I'm absolutely determined that this issue will be answered, will be put to bed."

"If there's any culpability in any area that is appropriate to be handled in some way with some discipline, it will be appropriately handled."

The White House has argued that all the circumstances of the attack were probed by a review board ordered by Clinton, and its recommendations acted upon.

"This is a subject that has, from its beginning, been subject to attempts to politicize it by Republicans, when in fact what happened in Benghazi was a tragedy," White House spokesman Jay Carney said.

U.S. officials said Kerry has asked for a staff briefing on the hearings when he returns to Washington, as he also awaits a report on what options are available if disciplinary action needs to be taken.