[WASHINGTON] President Barack Obama condemned the "horrific massacre" of 50 revelers at an Orlando nightclub Sunday, an attack that is already fueling rows over guns, gay rights and how to defeat the Islamic State group.
50 people were killed and 53 others wounded during a late-night assault on "Pulse," a nightclub popular with Florida's gay community.
Police have pinned the slaughter on 29-year-old Omar Mateen, a son of Afghan immigrants who is said to have pledged allegiance to IS before going on a rampage with an assault rifle.
"This was an act of terror and an act of hate," Mr Obama said in a sombre White House address to mark the worst mass shooting in US history.
"The shooter targeted a nightclub where people came together to be with friends, to dance, sing and live."
"As Americans, we are united in grief, in outrage, and in resolve to defend our people," Mr Obama said.
During his eight years in office, Mr Obama has had to appear publicly after more than a dozen mass shootings.
He has called the slaying of 20 children and six adults at Sandy Hook Elementary School in 2012, the worst day of his presidency.
But this latest shooting comes in the middle of a vitriol-filled campaign to see who will replace Mr Obama in the white House next year.
An Islamic State-inspired attack in San Bernardino, California in 2015 prompted Republican White House hopeful Donald Trump to call for a blanket ban on Muslims entering the United States.
That call was pilloried by many as racist and unconstitutional, but it propelled Mr Trump - now the Republican party nominee - to centre stage in the 2016 race.
The identity of the presumed Orlando shooter, his target and the fact that his weapons were legally purchased, will only fan the political flames.
Mr Trump is expected to focus a speech Monday on national security, rather than the alleged shortcomings of his rival Hillary Clinton as planned.
Meanwhile, a first joint campaign event between Democratic nominee Clinton and Mr Obama, scheduled for Wednesday, has been postponed.
In his statement, Mr Obama was careful not to inject too much politics into the issue.
"We've reached no definitive judgment on the precise motivations of the killer," he added, saying that the FBI was nonetheless threating the attack as an "act of terror."
"We must spare no effort to determine what, if any, inspiration or association this killer may have had with terrorist groups."
Mr Trump was quick to point out that Mr Obama has repeatedly refused to associate such attacks with Islam.
"Is President Obama going to finally mention the words radical Islamic terrorism? If he doesn't he should immediately resign in disgrace!" he said on Twitter.
The last week had offered Mr Obama a rare glimmer of hope in the fight against the Islamic State, with the group under series pressure in Libya and Syria.
Democrats have honed in on evidence that Mateen bought two weapons legally in recent days to call for tighter gun control.
"The shooter was apparently armed with a hand gun and a powerful assault rifle," Mr Obama said.
"This massacre is therefore a further reminder of how easy it is for someone to get their hands on a weapon that lets them shoot people in a school, or in a house of worship, or a movie theater, or in a nightclub."
"We have to decide if that's the kind of country we want to be. And to actively do nothing is a decision as well."
The flag at the White House was lowered to half-staff and Mr Obama ordered all government buildings to do the same.