President Trump on Monday expressed his condolences and sympathies to victims and families of the deadly mass shooting at a country music festival in Las Vegas.

"My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting," Trump tweeted. "God bless you!"

My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you! — Donald J. Trump (@realDonaldTrump) October 2, 2017

White House press secretary Sarah Huckabee Sanders said in a statement that Trump was briefed on the "horrific tragedy."

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“We are monitoring the situation closely and offer our full support to state and local officials," she added. "All of those affected are in our thoughts and prayers.”

At least 58 people are dead and 500 others are injured after gunfire broke out at the concert late Sunday.

Sheriff Joe Lombardo told reporters early Monday that the suspected gunman, identified as Stephen Paddock, 64, of Mesquite, Nev., fired from the 32nd floor of the Mandalay Bay. He was found dead in his room when officers breached its door.

Police believe this was a "lone wolf" attack.

The shooting happened during a country music festival that reportedly draws thousands of attendees.

White House officials said early Monday that Trump's planned trip to Puerto Rico on Tuesday is under review.

--This report was updated at 10:10 a.m.