US Vice President Mike Pence is to head an investigation into President Donald Trump's claims of massive voter fraud, Trump said in an interview with Fox News on Sunday (5 February).

"We're gonna look at it very, very carefully," the president said during an interview with Fox host Bill O'Reilly that aired on Sunday 5 February before the American football Super Bowl.

Moments earlier the president appeared to track back on his repeated and unsubstantiated claims that around three million people voted illegally in the 2016 election.

Trump insisted O'Reilly "forget" that he has said several times since the November 2016 election that voter fraud was carried out on a massive scale.

As recently as 27 January Trump claimed "at least 3,000,000 votes were illegal". He cited Gregg Phillips, head of the conservative True the Vote non-profit, who said he compiled the number of illegal votes soon after the election. Despite being asked repeatedly, Phillips has not yet revealed any evidence of how he arrived at that figure, or set a time for its release.

On 27 November Trump wrote on Twitter that he "won the popular vote if you deduct the millions of people who voted illegally". But on Sunday he insisted O'Reilly should "forget all of that" and "just take a look at the registration".

"I'm gonna set up a commission, to be headed by Vice President Mike Pence," Trump stated.

His claim regarding large-scale voter fraud has been proven false by officials and fact-checkers across the political spectrum. These include New Hampshire's Republican governor-elect who disputed the claim; PolitiFact, which is an offshoot of The Miami Herald and seven other newspapers; as well as Factcheck.org, a non-profit organisation. California's Secretary of State, Alex Padilla also said, "allegations of voter fraud in California and elsewhere are absurd".

A study of voting published in December 2016 by statisticians and political scientists at Dartmouth College did not "uncover any evidence consistent with Trump's assertions about widespread voter fraud".

O'Reilly urged Trump that "you've gotta have data" to back up claims over voter fraud.

"It doesn't have to do with the vote," Trump insisted. He continued: "Although that's the end result. It has to do with the registration. And when you look at the registration and you see dead people that have voted, when you see people that are registered in two states that voted in two states, when you see other things, when you see illegals, people that are not citizens, and they're on the registration rolls."

Trump seemed to allude to a 2012 Pew study that he often quoted on the campaign trail that found "more than 1.8 million deceased individuals are listed as voters". This indicates voter rolls are not being purged as regularly as they should be. The report identifies that America's voter registration system needs an upgrade, but it does not go as far as to say that the system is compromised and open to abuse.

"A lot of people have come out and said that I am correct," Trump told O'Reilly. He did not provide a timeline for when the Pence-led probe will begin.