The Foreign Affairs Minister Charlie Flanagan has said he is "shocked and horrified" after 10 people were killed in a mass shooting at a college in Oregon.
The gunman - named as Chris Harper Mercer (26) - attacked students inside a classroom.
He died in an exchange of fire with police in the city of Roseburg.
His social media posts show he supported the IRA, and he said he admired a man who shot dead a TV presenter live on air.
Minister Flanagan, who is in New York, says: "I am shocked and horrified by the news of the multiple fatalities that have occurred in this morning's appalling attack in Oregon".
"As I conclude my visit to the US, my thoughts are with the dead and injured students and their bereaved families".
While US President Barack Obama has made another impassioned plea for more gun regulation in the US.
Mr Obama says America must take action to stop incidents like this from happening.
"We spend trillions preventing terrorist attacks on our soil". Credit: The White House via Youtube
The President said "inaction" on gun control legislation makes all Americans "answerable" for the violence.
He added that the nation has become "numb" to mass shootings, which have become "routine" occurrences in America.
"As I said just a few months ago, and I said just a few months before that, and I said each time we see one of these mass shootings, our thoughts and prayers are not enough," he said.
"We are not the only country on Earth who has people with mental illnesses who want to do harm to other people".
"(But) we are the only advanced country on Earth who sees these kinds of mass shootings every few months".
"We are going to have to change our laws. This is not something I can do by myself".
"I need to have congress and state legislatures and governors who are willing to work with me on this".
A visibly angry Mr Obama said the issue of gun control should be politicised in America, and called on Americans to hold politicians accountable for acting on the issue.
He said he would continue to raise the need for gun control reform every time a shooting takes place in the US.
David Jaques of the Roseburg Beacon newspaper told Newstalk Breakfast Mr Obama was too quick to politicise this tragedy.
