US president Donald Trump has called the mass shooting in Las Vegas "an act of pure evil".
In a televised address, Mr Trump said the nation is joined together in sadness, shock and grief after the massacre which left at least 50 people dead and another 406 injured.
The American leader said he will visit Las Vegas on Wednesday to meet first responders and families of the victims.
Mr Trump said the nation must stay unified.
He added that although "we feel such great anger at the senseless murder of our fellow citizens, it is our love that binds us today and always will".
In a sombre, measured address, the US president praised first responders who he said prevented further losses of life.
He offered condolences to the families of those killed, saying: "We cannot fathom their pain. We cannot imagine their loss.
"We are praying for you. We are here for you."
Mr Trump said flags will be flown at half-mast to honour the victims until sunset on October 6.
Gunman: Stephen Paddock
The proclamation covers flags at the White House and all public buildings, military posts, naval stations and naval vessels throughout the United States and all territories. It also extends to embassies, military facilities and other sites overseas.
The president said he and first lady Melania Trump are praying for those who have been lost and wounded, and for "the entire nation to find unity and peace".
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