The US has backed away from its initial account of the killing of Osama bin Laden, which claimed that the al-Qaida leader was carrying a weapon and fired at US troops before he was shot dead.

On Monday, John Brennan, a counterterrorism adviser to Barack Obama, said Bin Laden was "engaged in a firefight" with his assailants and he did not know if he "got off any rounds". Other US officials briefed that he was firing at members of the US navy's elite Seal Team Six.

However, subsequent briefings by US officials suggest that, when confronted at the high-security complex in Abbottabad, Bin Laden did not have a weapon and did not fire at his assailants. With some questions being raised as to why Bin Laden was shot dead, and whether he was executed, rather than taken into custody, Brennan said: "If we had the opportunity to take Bin Laden alive, if he didn't present any threat, the individuals involved were able and prepared to do that."

Officials have continued to imply he offered resistance before he was shot but have not clarified the extent of that resistance, given that he apparently did not have a weapon. Bin Laden was shot once above the left eye and once in the chest. The Obama administration is considering whether to release photographs of his burial at sea.

There were additional changes to the original narrative offered by US officials. Reporters were initially told that one of Bin Laden's wives was killed while he was using her as a human shield, prompting headlines such as "Osama bin Laden killed cowering behind his 'human shield' wife". But it has since been clarified that Bin Laden's wife was shot in the calf and did not die in the assault, although another woman was killed. This change of account has also raised questions over whether Bin Laden's wife - or anyone else - was being used as a human shield.

One US official told Politico: "Two women were shot here. It sounds like their fates were mixed up. This is hours old and the full facts are still being ascertained as those involved are debriefed."

As well as amending the condition of Bin Laden's wife, US officials have also changed the name of which of his sons was killed during the raid. The dead son was initially named in press reports as Hamza, described in one article as Bin Laden's "presumed heir" to the leadership of al-Qaida, apparently based on the official White House transcript of a Brennan briefing. However, Brennan said during the briefing that it was another son, Khalid, who was killed.

Qualifying the narrative of the assault that he offered to reporters, Brennan explained that some of the information came from live video feeds of the raid. "I wasn't there," he said.