Republican critics of Hilary Clinton have released selected testimony from a forthcoming hearing on the Benghazi embassy attack which appears to show that special forces and fast jets could have arrived in time to protect US diplomats.

As the political fallout from the September 2012 incident continues to dog Clinton, the former secretary of state, a witness due to speak before the House oversight committee on Wednesday alleges that military commanders blocked deployment of troops or planes for fear of offending the new Libyan government.

Gregory Hicks, the former deputy chief of mission in Libya, told a congressional interview in pre-prepared testimony that he believed the arrival of special forces or jets could have saved lives or even prevented the attack, which led to the death of ambassador Christopher Stevens and three others.

The White House declined to comment, stressing that it was an interview it had not yet been able to view. It was also not possible to verify whether the selected testimony from Hicks released on Monday was a partial version designed to emphasise critical aspects.

It does, however, shed important new light on attempts to dispatch troops to Bengazi:

Hicks: So, Lieutenant Colonel Gibson, who is the Socafrica commander, his team – you know – they were on their way to the vehicles to go to the airport to get on the C-130 when he got a phone call from Socafrica, which said: you can't go now, you don't have authority to go now. And so they missed the flight. And, of course, this meant that one of the ... Questioner: They didn't miss the flight. They were told not to board the flight. Hicks: They were told not to board the flight, so they missed it. So, anyway, and yeah. I still remember Colonel Gibson – he said: "I have never been so embarrassed in my life that a State Department officer has bigger balls than somebody in the military." A nice compliment.

The testimony also raises questions about whether US officials in Washington and Libya were too cautious in responding to the attack, which is thought to have been carried out by fighters close to al-Qaida.

White House spokesman Jay Carney acknowledged that there had been mistakes made before the attack, but insisted these had been dealt with in subsequent investigations.

"There was an accountability review board chaired by two of the most distinguished experts in our national security establishment, nonpartisan experts – Admiral Mullen and Ambassador Pickering – who oversaw this review," said Carney.

"And it was unsparing. It was critical. And it held people accountable. And it made a series of recommendations for action that could be taken to improve security to reduce the potential for these kinds of events from happening in the future. And every single one of those recommendations has been or is being implemented by the State Department."

Nonetheless, Wednesday's hearing looks set to re-open the issue both for the White House and for Clinton, who is still widely tipped to be planning a presidential run at the next election.

Pressure is likely to focus on what steps the US took once it was aware the embassy was under attack, an issue the selected Hicks testimony suggests was badly handled:

Questioner: But do you think, you know, if an F-15, if the military had allowed a jet to go fly over, that it might have prevented [the second attack]? Hicks: Yeah, and if we had gotten clearance from the Libyan military for an American plane to fly over Libyan airspace. The Libyans that I talked to and the Libyans and other Americans who were involved in the war have told me also that Libyan revolutionaries were very cognizant of the impact that American and NATO airpower had with respect to their victory. They are under no illusions that American and NATO airpower won that war for them. And so, in my personal opinion, a fast-mover flying over Benghazi at some point, you know, as soon as possible might very well have prevented some of the bad things that happened that night. Questioner: The theory being, the folks on the ground that are doing these – committing these terrorist attacks look up, see a heavy duty airplane above, and decide to hightail it? Hicks: I believe that if – I believe if we had been able to scramble a fighter or aircraft or two over Benghazi as quickly as possible after the attack commenced, I believe there would not have been a mortar attack on the annex in the morning because I believe the Libyans would have split. They would have been scared to death that we would have gotten a laser on them and killed them.

The hearing will also include testimony from Mark Thompson, acting deputy assistant secretary for counterterrorism, and Eric Nordstrom, a diplomatic security officer and former regional security officer in Libya.

In October 2012, the Oversight committee held the first hearing on the Benghazi attacks, which it says exposed denials of security requests and forced the administration to acknowledge that the attacks were not sparked by a protest of a YouTube video, contrary to claims made by Obama administration officials.