With seven weeks to go before the first nominating contest in Iowa, Trump, 69, has held or expanded his lead in national polls in the Republican race for the November 2016 presidential election but seen Cruz, 44, move past him in some Iowa surveys, making their debate encounter potentially combustible.

A conservative US senator from Texas, Cruz has tried to avoid direct confrontation with Trump, but Cruz's rise in the polls could make him a target for the combative billionaire at the nationally televised forum from Las Vegas.

Trump called Cruz a 'maniac' on Sunday, an indication that he is prepared to attack Cruz as he has other rivals.

Trump's unpredictable and controversial rhetoric has repeatedly put him at center stage in the Republican race. He has dominated the campaign with his call for a total ban on Muslims entering the United States, following a married couple's Dec 2 massacre of 14 people in San Bernardino, California, inspired by Islamic State.

Most of his Republican rivals, as well as officials and leaders in the United States and around the globe, have criticized Trump's proposal although many of his supporters have voiced sympathy with his views.

Also appearing in the main debate are New Jersey Governor Chris Christie, Ohio Governor John Kasich, US Senator Rand Paul of Kentucky and former corporate executive Carly Fiorina.

Click here for more news on Donald Trump

Latest News from World News Desk