LAS VEGAS: America mourned the victims of the worst gun massacre in recent US history on Tuesday as investigators probed the motive behind an apparently senseless attack on Las Vegas concert-goers.

President Donald Trump branded the attacker who raked a crowd of thousands with gunfire from a 32nd-floor hotel room, leaving 59 dead and at least 527 injured a `demented man`. But beyond that diagnosis, authorities were at a loss as to why the 64-year-old gambler and retired accountant had hauled a vast arsenal of weapons to the hotel and launched his assault.Meanwhile, a grim parade of victims began to be identified in the media, each new name stirring emotions as America once again grappled with calls by lawmakers for reforms to permissive firearm control laws and angst over its pervasive gun culture.

Trump, questioned by reporters as he left the White House to survey hurricane relief in Puerto Rico, was not ready to suggest answers.

`What happened in Las Vegas is in many ways a miracle,` he said.

`The police department has done such an incredible job, and we`ll be talking about gun laws as time goes by.` US officials have reacted cautiously to a claim by the Islamic State militant group that the shooter, Stephen Craig Paddock, had carried out Sunday night`s massacre on its behalf.

Experts cautioned that the group under pressure in its Syrian andIraqi heartlands may be trying to rally its supporters with a false claim.

In a statement, IS claimed Paddock was one of its `soldiers` but the FBI said it had found no such connection so far and the local sheriff described him as a lone `psychopath`. Police said Paddock, who had no criminal record, smashed windows in his hotel room shortly after 10pm on Sunday and trained bursts of fire on a crowd attending a country music concert down below.

In footage of the massacre broadcast on TV news, the sustained rattle of gunfire is heard as people scream and bolt for cover with little idea of where the shots were coming from.

`We saw bodies down. We didn`t know if they had fallen or had been shot,` said Ralph Rodriguez, an IT consultant from Pomona Valley near Los Angeles.`People started grabbing their loved-ones and just strangers, and trying to help them get out of the way,` he said.

Sheriff Joseph Lombardo said Paddock Kred through the door of his hotel room and hit a security guard in the leg.

But when a SWAT team stormed the room where Paddock had been staying since September 28, they found he had killed himself.

Inside the room were 23 firearms, including automatic weapons, he said.

Investigators also found another 19 firearms along with explosives and several thousand rounds of ammo at Paddock`s house.

Lombardo said they had discovered several pounds of an explosive called tannerite at the house as well as ammonium nitrate, a type of fertiliser, in his car.-Agencies