US presidential candidate Donald Trump appeared to re-up his call for a ban on Muslims entering the US on Monday after a reportedly Muslim man killed at least 50 people at a gay club in Florida.

"What has happened in Orlando is just the beginning. Our leadership is weak and ineffective. I called it and asked for the ban. Must be tough," Trump wrote on Twitter, even though the Orlando shooter, Omar Mateen, was born in the US and therefore would not be affected by such a ban.

What has happened in Orlando is just the beginning. Our leadership is weak and ineffective. I called it and asked for the ban. Must be tough — Donald J. Trump (@realDonaldTrump) June 12, 2016

Mateen, 29, was born in New York to Afghan parents, according to ABC News. He worked for a security company in Florida, had two firearms licenses, and was said by his ex-wife to be violent and mentally-unstable.

@realDonaldTrump he was an American citizen, just like you — Alan Yuhas (@AlanYuhas) June 12, 2016

Mateen reportedly pledged allegiance to Daesh, or Islamic State, in the middle of the attack on Orlando's Pulse nightclub.

Trump famously called for a "complete and total shutdown" on Muslims entering the US after a deadly shooting by a Muslim couple in San Bernardino, California, in December.

Since then, however, he's backpedaled, saying last month that it was only "a suggestion."

--HS