Donald Trump raises the issue of his main rival's birthplace in a fractious TV debate between the Republican White House hopefuls.

Republican frontrunner Donald Trump has questioned whether his main rival Ted Cruz should be allowed to stand for President.

He said the fact that the Texas Senator was born in Canada raises questions about his eligibility.

"There's a big question mark over your head," he told him during the latest televised debate for White House hopefuls.

Under the constitution the President of the United States must be a "natural born citizen".

Mr Cruz replied that the definition of "natural born citizens" included people with an American parent such as himself.

He was born in Calgary to an American mother and a Cuban father.

He said: "You know, back in September, my friend Donald said that he had had his lawyers look at this from every which way and there was no issue there. There was nothing to this 'birther' issue.

"Now, since September, the constitution hasn't changed, but the poll numbers have."

But Mr Trump refused to budge, saying a Harvard law scholar had raised doubts about the issue and Mr Cruz could face lawsuits from Democrats.

"The fact is, there's a big overhang, there's a big question mark on your head, and you can't do that to the party," he said.

"You have great constitutional lawyers that say you can't run. I'm not bringing a suit, I promise, but the Democrats are going to bring a lawsuit."

Mr Cruz replied: "I've spent my entire life defending the constitution before the US Supreme Court, and I'll tell you I'm not going to be taking legal advice from Donald Trump."

The debate in North Charleston comes just two weeks before the first real test of the campaign, when voters in Iowa pick their Republican and Democratic choices for president.

Mr Cruz is leading some of the polls there.

Hosted by Fox Business Network, the debate saw the other candidates attack President Barack Obama's State of the Union address earlier this week.

"Tuesday night I watched story time with Barack Obama, and I've got to tell you, it sounded like everything in the world was going amazing," quipped New Jersey Governor Chris Christie to laughs from the audience.

The other candidates on stage were Florida Senator Marco Rubio, former Florida Governor Jeb Bush, Ohio Governor John Kasich and retired neurosurgeon Ben Carson.

Source: Sky News