Donald Trump, 2016 Republican presidential nominee, speaks during a campaign rally at the Erie Insurance Arena in Erie, Pennsylvania, U.S., on Friday, Aug. 12, 2016.

U.S. actor and producer Robert De Niro said on Saturday that U.S. Republican presidential candidate Donald Trump should not run for president because he was "totally nuts".

Trump, a billionaire businessman seeking his first public office, has courted controversy with a string of inflammatory statements about his main opponent Hillary Clinton, guns, Mexicans, Muslims and war veterans, among others.

De Niro made the comments to a Sarajevo audience as he presented a digital version of Martin Scorsese's film "Taxi Driver", in which he starred, to mark its 40th anniversary.

"I don't know, it's crazy that people like Donald Trump ..., he shouldn't even be where he is, so God help us," De Niro said to wide applause in the Sarajevo National Theater.

"What he's been saying is really totally crazy, ridiculous ... he is totally nuts."