More details of the gun attack on a gay club - where 49 people were killed - have been revealed by authorities in Orlando, Florida.
The deadliest mass shooting in recent US history ended with gunman Omar Mateen being killed himself. The attack also left 53 people injured.
After Mateen holed up in a toilet with hostages at the Pulse club, police tried to blow a hole in a wall.
When that failed, they used a Bearcat armoured vehicle to break through.
Orlando Mayor Buddy Dyer praised the "heroic acts" of the city's police department, law enforcement agencies and citizens.
The authorities made clear that the death toll from the shooting was 49; an earlier figure of 50 included the gunman, who was shot dead by police.
An off-duty officer working at the club had initially fought Mateen in a gun battle. Shortly after, more police officers arrived.
They engaged Mateen, forcing him to retreat to the toilet, where he was holding hostages, Orlando police chief John Mina said.
Mateen phoned the police from the toilet, Mr Mina said, and made a pledge of allegiance to the so-called Islamic State group (IS) while speaking to them.
Chief Mina said that statements made by the suspect while he was holed up in the toilet, and information from people trapped inside, had convinced police that further loss of life was imminent.
After officers broke through the wall, "dozens and dozens" of people emerged from the hole, the police chief said.
Mateen himself came out shooting and was killed, he added.
'No clear evidence' of IS link
There was no clear evidence that the Orlando shooter was directed by the so-called Islamic State group (IS), said US President barack Obama.
The inquiry into Sunday morning's attack was being treated as a terrorist investigation, he said.
Speaking in Washington, the president said: "It does appear that at the last minute he [gunman Omar Mateen] announced allegiance to Isil [IS].
"But there is no evidence so far that he was in fact directed.
"This is certainly an example of the kind of home-grown extremism that all of us have been concerned about for a very long time," Mr Obama said.
Killer not on watch list
Mateen, a US citizen of Afghan descent who was born in New York and lived in Florida, was not on a terrorism watch list.
However, the FBI interviewed him twice in 2013-14 after he made "inflammatory remarks" to a colleague, before closing its investigation.
Mateen had legally purchased several guns in the days before the attack.
Seddique Mateen, the father of the gunman, said he did not know that his son had a "grudge in his heart" and did not understand why his son had carried out the shooting.
A statement on the IS-affiliated Amaq news agency said an IS "fighter" was responsible and on Monday, the group's al-Bayan radio called Mateen "one of the Caliphate's soldiers in the US".
A security company that Mateen used to work for said he had been vetted twice.
The checks in 2007 and 2013 did not reveal anything of concern, G4S said, and Mateen had carried a gun as part of his job.
Ex-wife: Mateen was 'disturbed'
Sitora Yusufiy lived with Mateen for four months in 2009. She said her family had "rescued" her from the relationship when they became aware he was being physically abusive.
He beat her up regularly during their short-lived marriage for trivial things like not doing laundry, she said.
"When he would get in his tempers, he would express hate toward everything. He was mentally unstable and mentally ill: that's the only explanation that I could give."
Earlier, President Obama called the attack an "act of terror" and an "act of hate".
The presumptive Republican presidential nominee Donald Trump said on Monday that the US needed to stop the flow of Syrian refugees to prevent such attacks.
He also blamed the Muslim community for not reporting Mateen to the authorities, despite suspicions that he was a "whack job".
People knew it was going to happen but they did not report him, he said.
The death toll means that the Orlando attack surpasses the 2007 massacre at Virginia Tech, which left 32 people dead.
According to the crowd-sourced Mass Shooting Tracker, the US suffered 372 mass shootings last year, defined as a single incident that kills or injures four or more people. Some 475 people were killed and 1,870 wounded.
Cities around the world have been flying rainbow gay pride flags and illuminating buildings in solidarity with the victims of the shooting in Florida.