MANCHESTER (AFP) - White House hopeful Donald Trump vowed on Monday to "suspend immigration" from nations with links to terror attacks targeting the United States or its allies, one day after a Florida nightclub massacre.

"When I'm elected, I will suspend immigration from areas of the world where there is a proven history of terrorism against the United States, Europe or our allies, until we fully understand how to end these threats," Trump said during a national security speech in New Hampshire.

"We cannot continue to allow thousands upon thousands of people to pour into our country, many of whom have the same thought process as this savage killer." Trump rapped his likely opponent in the US presidential race, Democrat Hillary Clinton, by saying she is pushing to expand immigration and the nation's refugee program to allow more Syrians into the United States.

"Clinton wants to allow radical Islamic terrorists to pour into our country," he said, highlighting how such extremists have enslaved women and murdered homosexuals.

"Immigration is a privilege, and we should not let anyone in this country who doesn't support our communities." Speaking of the Orlando shooter, who was born in New York to Afghan parents, Trump said "the only reason the killer was in America in the first place was because we allowed his family to come here."

He added: "We have a dysfunctional immigration system which does not permit us to know who we let into our country."

Trump's blunt comments come six months after he controversially called for a ban on Muslims entering the United States.

He also expressed strong support for America's gay community, following Sunday's attack on the gay nightclub in Orlando left 50 people dead including the shooter.

"This is a very dark moment in America's history," Trump said.

"It's a strike at the heart and soul of who we are as a nation," he added.

"It's an assault on the ability of free people to live their lives, love who they want and express their identity."