The White House said Monday it would be "premature" to reopen the US debate on tighter gun controls in the wake of the mass shooting that left 58 people dead in Las Vegas.

"There's a time and place for a political debate, but now is the time to unite as a country," Press Secretary Sarah Sanders told the daily White House briefing.

"A motive is yet to be determined and it would be premature for us to discuss policy when we don't fully know all of the facts or what took place last night