Republican presidential candidate Rand Paul has fanned the birther flames against 2016 rival Ted Cruz, calling into question his birthplace and, therefore, his eligibility for the White House by saying the Texas senator is a "natural-born Canadian."

"I think without question, everybody would accept that, you know, Cruz is a natural-born Canadian, that he was naturally born there," Paul said in an interview on Fox News on Monday, according to The Hill. "The question is can you be a natural-born Canadian and a natural-born American at the same time, maybe, but I think the courts will have to decide it, because it's never really been decided."

Paul insisted that he was not instigating a court battle but rather just stating the facts that Democrats will do so. 

"Democrats have already threatened. There is one Democratic congressman who said he will file a lawsuit over this," Paul said, referring to Rep. Alan Grayson (D-Fla.), according to CNN. "It is not me, it's whether or not Democrats pursue it - and I think they will."

Paul said that while there is no question Cruz is a U.S. citizen, there is a question as to what the Constitution requires for presidential eligibility and that the Supreme Court will likely have to weigh in. 

"For traditional citizenship it always has been (your parent), but the only part of the Constitution that says 'natural-born' is with regard to the president. So it appears to be a unique qualification and most people have interpreted they had to be born in the U.S. until recently," Paul said, according to TPM. "So I think eventually the Supreme Court will probably have to decide it."

Questions about Cruz's eligibility for the White House have been in circulation for some time. However, it was when Republican presidential front-runner Donald Trump raised the issue that it gained steam. 

"Republicans are going to have to ask themselves the question: 'Do we want a candidate who could be tied up in court for two years?' That'd be a big problem," Trump told The Washington Post, referring to the Texas senator. "It'd be a very precarious one for Republicans because he'd be running and the courts may take a long time to make a decision. You don't want to be running and have that kind of thing over your head." 

For his part, Cruz on Sunday said that although he was born in Canada, he is eligible by virtue of his mother's citizenship. "The Internet has all sorts of fevered swamp theories, but the facts are simple," Cruz responded, according to CNN. "My mom was born in Wilmington, Delaware. She was an American citizen by birth. She's been an American citizen all 81 years of her life. She's never been a citizen of any other place."