At least 49 people were killed and at least 53 more injured in what is now the deadliest shooting in American history. According to CNN, the shooter, identified as Omar Mateen, pledged allegiance to ISIS during a 911 call moments before he opened fire inside the Pulse night club. Pulse is a popular gay club in the city. Mateen was killed in a shootout with police.

In a statement his afternoon, President Barack Obama said the shooting was an act of terror and hatred, adding,

Today, as Americans, we grieve the brutal murder—a horrific massacre—of dozens of innocent people. We pray for their families, who are grasping for answers with broken hearts. We stand with the people of Orlando who have endured a terrible attack on their city. This could have been any one of our cities. … 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, in a house of worship, or in a movie theater or in a nightclub. And we have to decide if that’s the kind of country we want to be. To actively do nothing is a decision as well.

We’ve got work to do when LGBT people around the world still face incredible isolation and poverty and persecution and violence, and even death. We have work to make sure that every single child, no matter who they are or where they come from or what they look like or how they live, feels welcomed and valued and loved …

In the coming hours and days, we’ll learn about the victims of this tragedy. Their names. Their faces. Who they were. The joy that they brought to families and to friends, and the difference that they made in this world. Say a prayer for them and say a prayer for their families—that God give them the strength to bear the unbearable. And that He give us all the strength to be there for them, and the strength and courage to change. We need to demonstrate that we are defined more—as a country—by the way they lived their lives than by the hate of the man who took them from us.

You can read his full statements here.

According to the FBI, Mateen was known to authorities and was investigated as recently as 2014. Mateen was born in the U.S.; his parents are from Afghanistan.

Prayers and messages of sorrow for the victims have poured in from around the world, including a statement from the Vatican, which said,

We all hope that ways may be found, as soon as possible, to effectively identify and contrast the causes of such terrible and absurd violence which so deeply upsets the desire for peace of the American people and of the whole of humanity.