The US attorney general has said al-Qaeda leader Osama Bin Laden was a lawful military target whose killing was "an act of national self-defence".
Eric Holder told a Senate committee that Bin Laden had made no attempt to surrender.
The US has acknowledged that Bin Laden was unarmed when shot dead in Monday's raid by US special forces in Pakistan.
Meanwhile, the White House has decided not to release photos of the dead Bin Laden.
Two couriers and one woman also died in Monday's assault, while one of Bin Laden's wives was injured.
"If he had surrendered, attempted to surrender, I think we should obviously have accepted that, but there was no indication that he wanted to do that and therefore his killing was appropriate," Mr Holder told the Senate Judiciary Committee.
Critics have raised concerns about the legality of the operation.
Washington has revised its account after initially saying Bin Laden was shot while taking part in a firefight as US Navy Seals stormed the compound.
More details have emerged of the information held on 10 computers, 10 mobile phones and 100 USB sticks, yielded by the US raid on the compound where Bin Laden was hiding.
Two telephone numbers and 500 Euros ($745; £450) were found stitched into Bin Laden's clothing in case he needed to make a quick getaway, says the BBC's Mark Mardell in Washington.
President Barack Obama, who watched the raid from the White House on monitors, saw his approval rating jump 11 points to 57% in a New York Times/CBS News poll on Wednesday.
He plans to visit the World Trade Center site in New York on Thursday to remember victims of the 11 September attacks, of which Bin Laden was said to have been the mastermind.
The Pakistani military has confirmed that it is holding survivors of the US special forces operation.
They were being kept at secret locations in the cities of Rawalpindi and Islamabad, said Pakistan army spokesman Maj Gen Athar Abbas.
Some of the survivors were being treated for bullet wounds that were serious but not life-threatening, he added.
The BBC's Aleem Maqbool says the compound where the raid unfolded has now become a sightseers' attraction.
There is an ice-cream vendor outside and children selling what they claim is wreckage from a US helicopter, which the Americans said they blew up after it apparently malfunctioned during the operation.