Citing unnamed US officials and witnesses, The Los Angeles Times said the attack, which killed ambassador Christopher Stevens and three other Americans, was "carried out following a minimum amount of planning".

"The attackers exhibited a high degree of disorganisation," the paper quotes one of the intelligence officials as saying.

"Some joined the attack in progress, some did not have weapons and others just seemed interested in looting."

According to another official cited by the paper, "There isn't any intelligence that the attackers pre-planned their assault days or weeks in advance."

Most of the evidence suggested that "the attackers launched their assault opportunistically" after learning about the violence at the US Embassy in Cairo, the report quotes the official as saying.

Top Republicans have said President Barack Obama's administration is reluctant to acknowledge the incident was an act of terrorism for political reasons.

But after five weeks of investigation, US intelligence agencies say they have found no evidence of al Qaeda participation, the newspaper said.

Aim to keep mission open

Newly released government documents show US officials intended to keep open a mission in Benghazi, Libya, for at least the rest of this year in hopes of having a “calming effect” on the region, before the building was overrun and burned by militants last month.

Locals in Benghazi wanted the Americans to stay permanently in the eastern Libyan city, the cradle of last year’s revolution against Muammar Gaddafi, according to one memo written by the former top US diplomat for the Middle East, Jeffrey Feltman.

The documents were made public on Friday by the House of Representatives Committee on Oversight and Government Reform, led by Republican Darrell Issa. It has been investigating the Sept. 11 assault on the US mission in Benghazi that took the lives of US Ambassador Christopher Stevens and three other Americans.

Other lawmakers raised more questions about the aftermath of the Benghazi events. The leading Republican on the Senate Intelligence Committee questioned why US spy agencies and government spokesmen initially played down suspected al Qaeda links to the September 11 attack on the mission there.

Administration officials ultimately declared the Benghazi incident to be a “deliberate and organised terrorist attack” carried out by “extremists” affiliated with or sympathetic to al Qaeda.

The Obama administration’s statements have “been strange from Day One on this,” the top Republican on the Senate Intelligence Committee, Saxby Chambliss, said in a telephone interview on Friday.

  Chambliss said the intelligence committee would investigate further. Another panel, the Senate Homeland Security Committee, sent letters on Friday to Secretary of State Hillary Clinton, Director of National Intelligence James Clapper and Defence Secretary Leon Panetta, demanding information about Benghazi.

The Benghazi attack has turned into election-year fodder in the United States, with Republicans charging that the Democratic Obama administration was caught unprepared for the assault, and Democrats claiming that Republicans are trying to exploit tragic events for political gain.

Issa wrote to President Barack Obama on Friday charging that his administration “has not been straightforward with the American people” in the aftermath of the Benghazi attack.

The top Democrat on the panel, Elijah Cummings, responded with a blast at Issa.

“It seems obvious that your goal in sending a public letter at this time is to release the most negative and distorted view possible of the attack in Benghazi ahead of the presidential debate on Monday evening,” Cummings said.

Obama is seeking re-election on Nov. 6 against Republican challenger Mitt Romney.

‘A salutary, calming effect’

Feltman’s memo, written Dec. 27 to Undersecretary of State Patrick Kennedy, urged the United States to continue its presence in Benghazi that began during the anti-Gadaffi revolt through the end of 2012.

In statements suggesting the US government felt it was making inroads in the region, Feltman said that staying in Benghazi would emphasize US interest in the eastern part of Libya, which he said sometimes feels ignored by Tripoli.

“Many Libyans have said the US presence in Benghazi has a salutary, calming effect on easterners who are fearful that the new focus on Tripoli could once again lead to their neglect and exclusion from reconstruction and wealth distribution and strongly favour a permanent US presence in the form of a full consulate,” said Feltman, the former assistant secretary of state for Near Eastern affairs.

Feltman is now UN undersecretary-general for political affairs.

Other dispatches released by the House committee on Friday included complaints about insufficient security in Benghazi. One US official in Libya said more security was needed to help protect American “outreach” efforts to the Benghazi populace.

A cable signed by Stevens about a month before he was killed focused on the deterioration of security in eastern Libya. It noted there had been an increase in violence in Benghazi but said it was not an organized campaign, and locals were determined to get through it.

“There have been abductions and assassinations, but there have also been false alarms and outright fabrications,” the August 8 cable said. “What we are going through — and what people here are resolved to get through — is a confluence rather than a conspiracy.”

“Attackers are unlikely to be deterred until authorities are at least capable,” the cable added.

Republicans have suggested the Obama administration omitted talking about al Qaeda in the days after Benghazi because this might undermine the administration’s claims to have weakened the organization with the killing of former leader Osama bin Laden.

“The administration omitted the known links to al Qaeda at almost every opportunity.  Whether this was an intentional effort by the administration to downplay the role of terrorist groups, especially al Qaeda, is one of the many issues the Senate Intelligence Committee must examine,” Chambliss said.

On Thursday, Senator Dianne Feinstein, the California Democrat who leads the intelligence committee, said talking points put out by Clapper may have contributed to the shifting commentary on Benghazi.

When asked why the US government initially played down the role of Islamic militants in the assault, she told KCBS-TV: “I think what happened was the director of intelligence, who is a very good individual, put out some speaking points on the initial intelligence assessment. I think that was possibly a mistake.”

US intelligence analysts summarized intelligence about the attack for public consumption in a September 15 document circulated to US policymakers and members of Congress.

The language in the public summary was virtually identical to language in a classified intelligence report circulated on September 12, according to multiple US government sources familiar with the matter. The secret document, however, reported that the extremists in question had possible links to al Qaeda — a point the unclassified document omitted.

White House spokesman Tommy Vietor said both assessments were prepared by members of the intelligence community and referred questions to them.