President Obama speaks to the nation in the aftermath of the Orlando shootings.

President Obama speaks to the nation in the aftermath of the Orlando shootings. White House

Obama Condemns ‘Most Deadly Shooting in American History’ as FBI Opens Probe

Islamic State news agency claims group is responsible for attack.

This article has been updated.

“Today marks the most deadly shooting in American history,” President Obama said as he addressed the nation from the White House in the aftermath of an attack in an Orlando nightclub in the early hours of Sunday that left about 50 people dead and another 53 wounded.

Obama stressed the FBI’s investigation was just beginning and he offered no details on the attacker’s motives or associations. “Although it is early in the investigation, we know enough to say this is an act of terror and an act of hate,” he said.

FBI agents are on the scene in Orlando and leading the probe of the mass shooting. “I’ve directed that the full resources of the federal government be made available for this investigation,” Obama said.

Obama added:

We are still learning all the facts. This is an open investigation We’ve reached no definitive judgment on the precise motivations of the killer. The FBI is appropriately investigating this as an act of terrorism, and I’ve directed that we spare no effort to determine what, if any, inspiration or association this killer may have had with terrorist groups. What is clear is that he was a person full of hatred.

The gunman has been identified as Omar Siddiqui Mateen, a U.S. citizen of Afghan descent living in Port St. Lucie, Florida. Officials described him as well-armed and well-prepared. He worked as a professional security officer and had a license to carry a firearm.

The Islamic State’s news agency issued a statement claiming responsibility for the attacks.

FBI Special Agent Ronald Hopper said Mateen died in an exchange of gunfire at the Pulse nightclub. Mateen, who was born in New York, was an American citizen of whom the bureau had been aware since 2013. He’d been investigated and questioned in 2013 and 2014, but the FBI didn’t find enough to merit a continued investigation of Mateen, Hopper said.

Hopper said Mateen had made 911 calls before his death. He declined to elaborate on the content of those calls, but said they had “become federal evidence [and] ...it was general to the Islamic State.” News reports had previously said Mateen had in the 911 calls pledged allegiance to ISIS, as the group is also known.

Trevor Velinor, an assistant special agent from the Bureau of Alcohol, Tobacco, Firearms, and Explosives, said Mateen had legally purchased both of the weapons used in the attack in the past few days.

Obama expressed "profound gratitude to all the police and first responders who rushed into harm’s way. Their courage and professionalism saved lives, and kept the carnage from being even worse. It’s the kind of sacrifice that our law enforcement professionals make every single day for all of us, and we can never thank them enough."

Obama ordered that flags be flown at half-staff at the White House, all public buildings and military posts in the United States, along with military and diplomatic facilities abroad.

While Obama did address gun violence in general in his address, he spoke with a sense of resignation about the intractable debate over gun control. “This massacre is … 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,” he said. “And we have to decide if that's the kind of country we want to be. And to tactically do nothing is a decision as well.”

“In the face of hate and violence, we will love one another,” Obama said. “We will not give in to fear and turn against each other.”

This article includes reporting from Quartz.