A day of mourning
- Vigils held across the US in memory of victims
- Empire State Building dims its lights to honour those killed
- Security stepped up at LGBT venues
- Killer had been interviewed by the FBI in 2013 and 2014
Vigils have been held across the United States after the deadliest mass shooting in its history targeted a gay nightclub in the state of Florida.
At least 49 people died and 53 were wounded in Sunday's shooting in Orlando with the rampage only coming to an end after perpetrator Omar Mateen was shot dead in a gun battle with police officers.
"Forty-eight of the 49 victims have been identified. Twenty-four of the next of kin have been notified with more to come," Buddy Dyer, the mayor of Orlando, said on Monday morning.
"We will not be defined by the act of a cowardly hater. We will be defined by how we respond, how we treat each other and this community has stepped up to do that," Dyer added.
Orlando Police chief John Mina described the shooting as "one of the worst tragedies we have seen", adding that police officers "were shaken by what they have seen inside the club".
"It's a tragedy not only for the city but the entire nation," he said. "Just a look into the eyes of our officers told the whole story."
The injured, many in critical condition, were transferred to nearby hospitals. Among those injured was one police officer, whose kevlar helmet was hit by a round from the suspect.
The suspect exchanged gunfire with a police officer working at the club, which had more than 300 people inside. The gunman then went back inside and took hostages, Mina said.
At around 5am, authorities sent in a SWAT team to rescue the hostages.
Ron Hopper, special FBI agent in charge of the Orlando office, confirmed that Mateen was interviewed twice by the agency in 2013, after he made "inflammatory comments" to co-workers alleging possible "terrorist ties".
In 2014, authorities interrogated Mateen anew for possible ties to an American suicide bomber.
In both cases, the FBI closed the investigations as they turned out to be "inconclusive" at that time, Hopper said.
Hopper also confirmed media reports that Mateen made 911 calls to police early on Sunday, and referred to the Islamic State of Iraq and the Levant (ISIL also known as ISIS) group.
Honouring the victims
Late on Sunday, mourners gathered near the target of the attack, the Pulse nightclub, as well as landmarks in other cities.
In New York, the Empire State Building went dark to honour the victims, while One Trade Center lit up its spire in the colours of the gay pride flag.
READ MORE: Who was Omar Mateen?
New York Mayor Bill de Blasio announced that all flags would be flown at half-mast in the city and that security measures have been strengthened, in particular around places associated with the LGBT community.
De Blasio told reporters that the shooting, which also left dozens injured, was "against our values".
But "you'll see a lot of additional police presence on the streets of the city," he added.
"No city in the world is better prepared to stop terror, to stop hate."
Hundreds of people gathered on Sunday evening in Greenwich Village to reflect on the violence and leave flowers, candles and letters beside a sign reading "Stop Hate".
|One World Trade Center's spire was lit up with the colours of the gay pride flag [EPA]
'A person filled with hatred'
Earlier, US President Barack Obama condemned the shooting as "an act of terror and an act of hate", calling the shooter "a person filled with hatred".
"As Americans, we are united in grief and outrage," he said, adding that the attack was "a further reminder of how easy it is for someone to get their hands on a weapon" and commit violence in the US.
Florida Governor Rick Scott has declared a state of emergency in Orlando.
Al Jazeera's Patty Culhane, reporting from Orlando, said politicians from opposite sides of the spectrum would be reacting in very different ways.
"It's been less than 24 hours but this is going to become a political issue ... what we're going to see is Democrats wanting to put the emphasis on [banning] semi-automatic weapons," Culhane said.
"The Republicans are going to try taking advantage of the fact that people are scared of the Islamic State of Iraq and the Levant ... so we're going to see [Democrats and Republicans] put the emphasis on two very different things."
The nightclub shooting came just a day after a man thought to be a deranged fan fatally shot Christina Grimmie, a rising singing star who gained fame on YouTube and as a contestant on The Voice, while she was signing autographs after a concert in Orlando.
The attacks were the worst in the US since the September 11 attacks carried out by al-Qaeda in 2001.
Source: Al Jazeera and agencies