A key US congressman has urged President Barack Obama to release the intelligence data that led US officials to describe the Benghazi, Libya attack as a spontaneous reaction to an anti-Islam film and not premeditated terrorism.

Obama, battling a tight race for re-election, has come under fire from Republicans who accuse his administration of huge security failures and of trying to cover-up the circumstances of the assault on a US consulate.

In a letter to Obama released Saturday, House Homeland Security Committee chairman Peter King, a Republican, urged the president to "release the intelligence community reporting which led your administration to characterize the assault ... as a 'spontaneous reaction' to a film trailer posted on the Internet."

He also called for Obama to release subsequent intelligence analysis "which led your administration to determine that the events of September 11, 2012 represented a terrorist attack."

King cited Vice President Joe Biden's recent pledge to "get to the bottom" of the Benghazi attack, which left four Americans dead including US ambassador Christopher Stevens.

He also referred to Biden's claim that the administration blamed the attack on a protest because that was the word from the intelligence community, and that as more facts were learned, they changed their assessment.

King is seeking intelligence agency transcripts, State Department radio traffic, instant messages, emails, cables, "tear lines" from situation reports, intercepts and any images which helped officials make their determinations.

Obama on Thursday denied that there had been "confusion" in his administration over the attack, after Republicans including King seized on the shifting narrative coming from US officials.

"I wasn't confused about the fact that we had to investigate exactly what happened so it gets fixed," he told Comedy Central's "The Daily Show" on Thursday.

"And I wasn't confused about the fact that we're going to hunt down whoever did it."