President Barack Obama says the Orlando nightclub shooter was a 'home-grown extremist'.
Omar Mateen killed 49 people and wounded 53 others at a gay nightclub in Florida yesterday.
The 29-year-old claimed allegiance to Islamic State in a 911 call.
However Mr Obama said he did not believe that that was the only motivation.
"Regardless of the particular motivations of this killer, there are connections between this vicious, bankrupt ideology and general attitudes towards gays and lesbians," he said.
President Obama has said there were no clear evidence Mateen was directed to carry out his assault or was part of a larger plot.
He said it appeared the shooter was inspired by extremist information obtained over the internet.
Meanwhile, police have revealed how they blasted their way into the Pulse nightclub in a desperate bid to end Omar Mateen's gun rampage.
Orlando Police Chief John Mina said Mateen had twice evaded police attempts to stop his attack on the packed gay nightclub - before holing up in the toilets with hostages.
Expert negotiators were drafted in to persuade the Islamic State sympathiser to give himself up - but a rescue attempt was launched after Mateen claimed he had a bomb and would kill more innocent clubbers "imminently".
Chief Mina said he gave the order for police to use explosives and a BearCat armoured vehicle to smash a hole in the wall big enough for some of those trapped in the club to escape through.
Moments later Mateen emerged from the same hole and was shot dead by a team of "eight or nine" officers after he opened fire on them with a handgun and long gun.
The shooting was America's deadliest terror attack since 9/11.
US authorities have confirmed he was able to buy at least two guns in the days before the attack - despite confirmation from the FBI that he had been interviewed twice over possible terror links.
Friends and co-workers have described Mateen as homophobic and "mentally unstable," while his ex-wife said he was violent and had biploar disorder.
Chief Mina said an off-duty Orlando officer working at Pulse nightclub had a gun battle with Mateen after he first opened fire in the venue at around 2am on Sunday morning.
A second gun battle followed when Orlando PD reinforcements arrived - forcing the gunman to retreat to the toilets at the back of the venue - and allowing police to rescue "dozens and dozens" of people from the nightclub's main room.
"We were able to rescue dozens and dozens of people"
#PulseShooting @ChiefJohnMina on what led to decision to breach walls of club and go in. #OrlandoUnited pic.twitter.com/CiPGgGXvsS
— Orlando Police (@OrlandoPolice) June 13, 2016
Police secured the building but it soon became clear that negotiations with Mateen - who had pledged allegiance to IS in a 911 call - were leading nowhere.
Chief Mina said: "He wasn't really asking for much. We were doing most of the talking.
"Based on statements made by the suspect and from information received from the suspect and hostages, we believed further loss of life was imminent, so I made the decision to commence the rescue operation and do the explosive breach.
"The explosive breach did not penetrate the wall completely. We used a BearCat armoured vehicle to punch a hole in that wall so there was a hole in that wall about 2ft off the ground and two-and-a-half/3ft wide and we were able to rescue dozens and dozens of people that came out of that hole.
"The suspect came out of that hole himself armed with a handgun and a long gun, engaged in a gun battle with officers, in which he was ultimately killed."
Meanwhile, one witness has spoken of his guilt as he told how he and others blocked one of the club exits after they escaped to an enclosed alleyway at the side of the building.
Luis Burbano told ABC News: "We went to an alleyway, which was only for employees. Me and this random guy tried blocking the door because the shots were getting louder and closer.
"We blocked this door and we did hear banging and I pray it wasn't anyone trying to escape because I would feel guilty forever, but at that point there was about 20 people crammed in this alleyway just trying to escape."
