WASHINGTON (AFP) - A top Democrat said on Tuesday (Dec 4) that a Republican from North Carolina may not be allowed to take up his seat in the US House of Representatives next year unless irregularities surrounding the election are cleared up.

The close Nov 6 election in North Carolina's 9th Congressional District has been marred by allegations of ballot fraud on behalf of the Republican candidate Mark Harris.

Mr Harris defeated Democrat Dan McCready by 905 votes, according to preliminary results, but the state elections board has declined to certify the vote amid the fraud allegations.

Democratic Representative Steny Hoyer told The Washington Post and other news outlets on Tuesday that Mr Harris may be denied a seat in the incoming Congress until questions about the election are resolved.

"If there is what appears to be a very substantial question on the integrity of the election, clearly we would oppose Mr Harris being seated until that is resolved," said Mr Hoyer, who will serve as majority leader when the new House is seated in January.

"The House has, as you know, the authority over the propriety of the election," Mr Hoyer said. "This is a very substantial question; it ought to be resolved before we seat any member."

"I would hope that the North Carolina officials get to the bottom of this controversy," he said.

The North Carolina state election board is currently investigating the race and could potentially call for a new election.

According to press reports, a Republican operative collected incomplete absentee ballots from voters in at least one county.

Mr Harris reportedly won 61 per cent of the absentee ballots in rural Bladen County and it was the only county in the district where mail-in ballots favoured the Republican.

Cases of outright electoral fraud are quite rare in the United States despite claims by President Donald Trump following the 2016 presidential election that "millions" of people had voted illegally.