US lawmakers are set to hold hearings about the deadly September 11 assault on the mission in Benghazi, with disgraced former spy chief David Petraeus expected to testify.

The White House has mounting questions over the attack in Libya that killed four Americans, including a US ambassador Chris Stevens and two former Navy SEALs, with leading Republican senators calling for “Watergate-style” hearings.

Republican lawmakers have accused the administration of failing to explain why there was not adequate security at the compound and why it took several days to provide a coherent account of the attack, blamed on Islamist militants.

Petraeus was scheduled to testify on the matter before the revelations of his affair with biographer Paula Broadwell forced his shock resignation as CIA director last week, just three days after Obama’s re-election. The House intelligence committee announced late on Wednesday that Petraeus would testify behind closed doors today at 7.30am (1330 CET).

But Senator John McCain said Petraeus was lined up to testify earlier before the Senate Intelligence Committee, raising the prospect of multiple congressional appearances this week for the fallen former general.

Lawmakers from both parties, and from the Senate as well as the House of Representatives, have clamoured for Petraeus and others to speak at various classified hearings to learn more about the circumstances of the attack.

Obama has said he bears full responsibility for any failings connected to Benghazi and on Wednesday slammed Republican lawmakers for criticising US ambassador to the UN Susan Rice over her statements on the attack.

Petraeus – the most celebrated general of his generation, credited with turning the tide of the US war in Iraq – has admitted to having an affair with Broadwell, a married army reservist who wrote a fawning biography of him.

FBI agents uncovered the affair after Tampa socialite Jill Kelley complained of threatening emails they later traced back to Broadwell, who apparently viewed Kelley, a Petraeus family friend, as a competitor for his affections.

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