US President Obama has called the deadliest mass shooting in US history an "act of terror" and an "act of hate".
50 people were killed in the attack which took place at a gay nightclub in Florida - a further 52 were left injured.
Islamic State's news agency has released a statement saying that the 29-year-old gunman Omar Mateen, was an Islamic State fighter.
In a statement in the White House this evening, Mr Obama urged Americans to love one another in the face of hate and violence:
Meanwhile, hundreds of people have lined up at blood donation centres in Orlando to help those injured in the Pulse nightclub shootings.
President Obama has ordered flags at the White House and federal buildings to be flown at half mast as a mark of respect for the victims.
Police departments across the US have increased patrols around popular gay-friendly locations and venues.
Here at home, President Michael D. Higgins has sent his condolences to the families of the victims of the shooting in Orlando today.
In a statement he said "Our thoughts are with the people of Florida at this difficult time, the loss of innocent lives on such a horrendous scale is truly shocking and challenges us all".
He went on to say that he has spoken to US Ambassador to Ireland Kevin O'Malley, and personally conveyed his deepest sympathy with the people of the United States at this time."
Director of GLEN, Brian Sheehan, says it is unspeakable what has happened to innocent people;
We want to thank the community for your support. Food/drinks have been dropped off. We have plenty at command post. pic.twitter.com/2eV4vSk3hP
— Orlando Police (@OrlandoPolice) June 12, 2016
Pulse shooting: In hail of gunfire in which suspect was killed, OPD officer was hit. Kevlar helmet saved his life. pic.twitter.com/MAb0jGi7r4
— Orlando Police (@OrlandoPolice) June 12, 2016
At the scene of the shooting | Photo: Phelan M. Ebenhack / AP/Press Association Images
