By Kevin Liptak, CNN White House Producer
(CNN) -- President Donald Trump addressed the deadliest mass shooting in US history on Monday morning from the White House, calling it an "act of pure evil."
The gun attack on a country music festival Sunday in Las Vegas killed at least 50 people and injured more than 400 others.
"My fellow Americans, we are joined together today in sadness, shock and grief," Trump said from the Diplomatic Reception Room.
The massacre in Nevada is the worst domestic act of violence of Trump's presidency. He was briefed on the situation Monday morning by his chief of staff, John Kelly, and conveyed his initial condolences on Twitter.
"My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!" he wrote.
White House press secretary Sarah Sanders called the attack a "horrific tragedy" and said in a statement that the White House was "monitoring the situation closely."
As a candidate, Trump used the Orlando night club shooting -- until Monday, the worst mass shooting in American history -- as a data point in his push to temporarily ban Muslims from entering the United States.
"I said this was going to happen -- and it is only going to get worse," Trump said in a statement then.
Trump was criticized for immediately connecting the incident to radical Islamic terrorism, but later he was defiant when the shooter was identified.
"Appreciate the congrats for being right on radical Islamic terrorism, I don't want congrats, I want toughness & vigilance. We must be smart!" Trump wrote on Twitter in the aftermath of the Orlando shooting.
Little is known about the perpetrator of the Las Vegas attack. Authorities have identified 64-year-old Stephen Paddock as the gunman.
During the course of his presidency, Trump's predecessor Barack Obama responded to more than a dozen mass shootings. His responses ranged from angry, to emotional, to -- by the end of his term -- resigned.
On Monday, Trump was originally scheduled to speak at an event about regulatory reform, but his public remarks were canceled. Later in the day he's slated to meet with Republican governors and the prime minister of Thailand.
He still plans to travel on Tuesday to Puerto Rico to survey storm damage, the White House said.
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