WASHINGTON - US President Donald Trump on Monday described the mass shooting at a Las Vegas music festival as "an act of pure evil".

Trump made the televised address to the nation after a gunman killed more than 50 people and wounded hundreds more when he opened fire on a country music concert in Las Vegas on Sunday.

"Last night a gunman opened fire on a large crowd at a country music concert in Las Vegas, Nevada. He brutally murdered more than 50 people and was an act of pure evil," he said.

The US Department of Homeland Security said on Monday that an investigation is underway. "Increased security in and around public places and events may be experienced as officials take additional precautions," it said.

Trump also said he will visit Las Vegas on Wednesday to meet with first responders and families. Trump said the nation must stay unified. He said that although he "feels such great anger at the senseless murder of our fellow citizens, it is our love that binds us today and always will".

In its claim, Islamic State said that the gunman, 64-year-old Stephen Paddock, was a recent convert. It came after IS on Friday released an audio recording of what it said was its leader, Abu Bakr al-Baghdadi, calling on extremists in Syria and Iraq to "resist" their enemies.

But US officials said on Monday that there was no evidence that the shooter was tied to any international militant group, and Trump made no mention of the claim in his address.

Las Vegas authorities are calling for blood donations and setting up a hotline to report missing people in the wake of the mass shooting. Las Vegas police said on Monday that it will take time to identify all of the injured and dead.

Meanwhile, the US Homeland Security Department said there is no "specific credible threat" involving other public venues. Police have not yet determined a motive in the shootings.

Since Trump's inauguration, there have been other mass shootings, including one in Texas last month, in which a gunman killed eight and was fatally shot by police. But the Las Vegas attack is the deadliest on Trump's watch.

The president offered a measured, somber response in June, after a shooting at a congressional baseball practice that wounded five, including seriously injuring Representative Steve Scalise. But he has drawn criticism for more inflammatory reactions to other acts of violence.

After a shooting at a nightclub in Orlando that left 49 dead last year, he tweeted, "Appreciate the congrats for being right on radical Islamic terrorism". In the wake of a deadly terror attack in London in June, Trump targeted the city's mayor on Twitter, suggesting he wasn't taking the attacks seriously enough.

AFP - AP - Xinhua - Reuters