Erin Kelly

USA TODAY

WASHINGTON — President Obama on Sunday called the mass shooting in Orlando "an act of terror" and "an act of hate."

"We stand with the people of Orlando, who have endured a terrible attack on their city," the president said in a brief address to the nation.

While emphasizing that the motivations of the gunman are still under investigation, Obama said, "We know enough to say that this was an act of terror and an act of hate. And as Americans, we are united in grief and in outrage, and in resolve to defend our people."

As the FBI continues to lead the investigation of America's deadliest shooting, "We will go wherever the facts lead us," Obama said of the massacre that killed 50 people and wounded 53 others.

"We are still learning all the facts," the president said. "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 must 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 filled with hatred. Over the coming days, we’ll uncover why and how this happened."

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The president said that Sunday was "an especially heartbreaking day for all our friends — our fellow Americans — who are lesbian, gay, bisexual or transgender."

"The shooter targeted a nightclub where people came together to be with friends, to dance and to sing, and to live," Obama said. "The place where they were attacked is more than a nightclub — it is a place of solidarity and empowerment where people have come together to raise awareness, to speak their minds, and to advocate for their civil rights."

He called the attack "an attack on all of us."

"No act of hate or terror will ever change who we are or the values that make us Americans," Obama said.

While he did not explicitly call for more gun control measures, the president said the shooting underscores how easy it is for people in the United States to obtain deadly weapons.

"The shooter was apparently armed with a handgun and a powerful assault rifle," 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. And 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."

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Obama urged Americans to say a prayer for the victims and their families.

"God give them the strength to bear the unbearable," he said.

Americans, he added, "will not give into fear or turn against each other."

"As we go together, we will draw inspiration from heroic and selfless acts — friends who helped friends, took care of each other and saved lives," the president said. "In the face of hate and violence, we will love one another."

Obama issued a proclamation Sunday honoring the victims of the attack and ordering U.S. flags to be flown at half-staff at the White House and all public buildings and military bases until sundown Thursday. Ryan's office said the flag at the U.S. Capitol would also be flown at half-staff.

Orlando Police Chief John Mina said the attack began at 2:02 a.m. Sunday, when three police officers engaged the suspect in a gun battle outside the crowded Pulse Orlando gay nightclub. A hostage situation then took place inside, and a SWAT team was called in, Mina said. Police received updates from club-goers trapped inside, and decided to storm the club at about 5 a.m. The gunman, identified by authorities as Omar Mateen, was reported dead at the scene.