President Trump extended “condolences” early Monday to the victims of the “terrible” mass shooting on the Las Vegas strip, in his first public reaction to the tragedy.

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

The president is expected to speak publicly about the shooting later Monday morning, according to the White House.

With at least 50 people dead and more than 200 injured, the attack is now considered the deadliest mass shooting in modern U.S. history.

“The President has been briefed on the horrific tragedy in Las Vegas,” a White House official told Fox News early Monday. “We are monitoring the situation closely and offer our full support to state and local officials. All of those affected are in our thoughts and prayers.”

The suspect, who was killed, was identified as 64-year-old Stephen Paddock, a local resident. Authorities also said they were “confident” Paddock’s roommate, Marilou Danley, had been located. Officials previously described Danley as a person of interest.

Authorities said one on-duty officer was in critical condition and another was wounded in the shooting. Two off-duty police officers attending the concert were killed.

“This was obviously well-planned, they waited for a major, open air event, and obtained a room facing it,” retired FBI special agent and former national FBI spokesman John Iannarelli, who drove past the scene of the event just moments before the shooting took place, told Fox News. “I can see the flashing blue police lights from my hotel window.”

“They were well-trained,” Iannarelli said, noting the use of automatic weapons. “That’s not an easy task.”

Iannarelli also said “it is too early to tell” what the motive was. “Is this a lone wolf inspired by others? This is exactly the type of attack the U.S. has been fearing would come to our shores.”

Officials did not immediately reveal a motive.

First lady Melania Trump also offered her condolences on Twitter Monday morning.

“My heart and prayers goes out to victims, families & loved ones! #PrayForLasVegas,” she tweeted.

Fox News’ Kristin Brown and The Associated Press contributed to this report.