A man President Donald Trump promoted as an authority on voter fraud was registered to vote in three states during the 2016 presidential election, the Associated Press reported.

Gregg Phillips, whose unsubstantiated claim that the election was marred by three million illegal votes was tweeted by the president, was listed on the rolls in Alabama, Texas and Mississippi, according to voting records and election officials in those states. He voted only in Alabama in November.

In a post earlier this month Mr Phillips described “an amazing effort” by volunteers tied to True the Vote, an organisation whose board he sits on, who he said found "thousands of duplicate records and registrations of dead people"

Trump has made an issue of people who are registered to vote in more than one state, using it as one of the bedrocks of his overall contention that voter fraud is rampant in the US and that voting by three to five million immigrants illegally in the country cost him the popular vote in November.