President Donald Trump says the gunman behind the mass shooting in Las Vegas was "a very, very sick individual" but declined to call it domestic terrorism.
"We'll be talking about gun laws as times goes by," Mr Trump told reporters at the White House on Tuesday.
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Asked if the shooting was an act of domestic terrorism, he added: "He was a sick man, a demented man. Lot of problems, I guess, and we're looking into him very, very seriously."
The Sunday night shooting spree from a 32nd-floor window of the Mandalay Bay hotel is the deadliest mass shooting in modern US history, leaving at least 59 dead and another 527 injured.
Stephen Paddock, 64, left no immediate hint of his motive for the arsenal of high-powered weaponry he amassed, including 34 guns, or the carnage he inflicted on a crowd of 22,000 attending an outdoor country music festival.
Earlier Mr Trump described the shooting as "an act of pure evil" that had left the US feeling "sadness, shock and grief".
Mr Paddock was not known to have served in the military, or to have suffered from a history of mental illness or to have registered any inkling of social disaffection, political discontent or radical views on social media.
US officials also discounted a claim of responsibility by the militant Islamic State group.
Police believed Mr Paddock acted alone but were at a loss to explain what might have precipitated it.
"We have no idea what his belief system was," Clark County Sheriff Joseph Lombardo told reporters. "I can't get into the mind of a psychopath."
Paddock shared his house with reported Australian girlfriend Marilou Danley, who is in Toyko. Authorities want to speak to her upon her return to the US.
The bloodshed ended after police swarming the hotel closed in on the gunman, who shot and wounded a hotel security officer through the door of his two-room suite and then killed himself before police entered.
Police said 23 guns were found in Mr Paddock's suite, along with more than 10 suitcases.
Mr Lombardo said a search of the suspect's car turned up a supply of ammonium nitrate, a fertiliser compound that can be formed into explosives and was used in the 1995 Oklahoma City bombing of a federal office building that killed 168 people.
Police found another 19 firearms, some explosives and thousands of rounds of ammunition at Mr Paddock's home in Mesquite, about 145km northeast of Las Vegas, along with some electronic devices, including computers.
They also obtained a warrant to search a second house connected to Mr Paddock in Reno, Nevada.