By Eli Watkins, CNN
(CNN) -- President Donald Trump has been briefed on the shooting in Las Vegas, which has left at least 50 dead and 400 injured, White House press secretary Sarah Sanders said in a statement Monday morning.
Trump tweeted shortly after Sanders' statement, writing:
The President will address the nation Monday morning at 10:30 a.m. EST, a White House official said.
Sanders called the mass shooting a "horrific tragedy" in her statement.
"We are monitoring the situation closely and offer our full support to state and local officials," Sanders said. "All of those affected are in our thoughts and prayers."
White House chief of staff John Kelly briefed the President on the shooting, she said.
Attorney General Jeff Sessions was meeting with the FBI on Monday morning, a Justice Department official said. Sessions also spoke briefly with Clark County Sheriff Joe Lombardo and offered support, the official said, adding that the Las Vegas shooting was the "top priority" for the day.
Although an administration official told CNN the President's trip to Puerto Rico to survey the hurricane response there, which was planned for Tuesday, was under review, Sanders said later in the morning that the visit was still on.
Vice President Mike Pence issued a statement on Twitter, saying he and his wife were praying for the victims.
First lady Melania Trump tweeted her "heart and prayers" to the victims and those affected.
My heart and prayers goes out to victims, families & loved ones! #PrayForLasVegas— Melania Trump (@FLOTUS) October 2, 2017
Ivanka Trump, the President's eldest daughter and a top adviser, tweeted,
2:2 Our collective hearts are breaking for the victims and their families. ?? #lasVegas— Ivanka Trump (@IvankaTrump) October 2, 2017
Nevada politicians also responded Monday morning to the massacre, decrying the violence and offering thanks to first responders.
"Senseless, horrifying act of violence in Las Vegas tonight," Republican Sen. Dean Heller, who is from Nevada, tweeted. "Praying for all the victims & those impacted by the tragedy."
"Thankful for police and first-responders on the scene," Heller said.
Heller said he had spoken with Nevada Gov. Brian Sandoval and state Attorney General Adam Laxalt.
Nevada's Democratic Sen. Catherine Cortez Masto offered prayers to the victims and thanks to the first responders on Twitter.
"Praying for all those affected by this senseless tragedy. Thank you to all the first responders. I will continue to monitor the situation," Cortez Masto tweeted.
Sandoval, a Republican, called the shooting a "tragic & heinous act of violence" and offered his prayers.
"A tragic & heinous act of violence has shaken the #Nevada family. Our prayers are w/ the victims & all affected by this act of cowardice," he tweeted.
Sandoval said in a statement that he would be in Las Vegas to meet with law enforcement and first responders and to console victims, their families and friends.
Members of Nevada's House delegation offered their thoughts as well.
Democratic Rep. Ruben Kihuen thanked the first responders in a tweet, and Rep. Dina Titus, also a Democrat, said in a statement that her "heart aches for the victims, their loved ones and our community."
As the morning wore on, politicians from around the country extended their sympathies to the victims of the shooting and thanks to first responders.
Florida Republican Sen. Marco Rubio, whose state suffered a massive shooting in an Orlando nightclub last year, tweeted his prayers, and Connecticut Democratic Sen. Chris Murphy, who has kept up a drumbeat for gun control in response to the Sandy Hook Elementary School shooting in his state in 2012, tweeted, "Not again."
The state's senior senator, Democrat Richard Blumenthal, said, "The nation's conscience must be galvanized."
New York Democratic Sen. Kirsten Gillibrand went further than many of her counterparts, saying her heart was with the victims, but "thoughts and prayers" were not enough.
"We must act to prevent this from happening again," Gillibrand tweeted.
Former Arizona Democratic Rep. Gabby Giffords, herself a victim of gun violence along with several others after an assassination attempt in 2011, said on Twitter that "no person should endure the horror Las Vegas experienced last night."
House Majority Leader Kevin McCarthy called the shooting "a senseless tragedy."
The chamber's minority leader, Nancy Pelosi wrote on Twitter that she was "horrified and heartbroken."
Former President Barack Obama tweeted: "Michelle & I are praying for the victims in Las Vegas. Our thoughts are with their families & everyone enduring another senseless tragedy."
Former President Bill Clinton wrote, "Thinking of the victims and responders in Las Vegas. This should be unimaginable in America."
Foreign leaders sent their condolences on the shooting Monday morning. United Kingdom Prime Minister Theresa May responded on Twitter, as did London Mayor Sadiq Khan.
"PM -- The UK's thoughts are with the victims and the emergency services responding to the appalling attack in Las Vegas," May tweeted.
Khan tweeted, "A deeply sad day for the city of Las Vegas. London sends our condolences to the victims and their families."
Canadian Prime Minister Justin Trudeau said, "Words fail this morning. The friendship & support of Canadians is with the victims in Las Vegas & the people of the US."
Police said in the early hours of Monday morning that the suspected gunman, identified as Stephen Paddock, 64, had been killed following what has now become the deadliest mass shooting in US history. At least 50 people died and 400 were injured, police said.
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