A top election official has dismissed US President Donald Trump’s fresh claims of voter fraud as rival Joe Biden edges closer to victory.

Mr Trump launched a flurry of unsubstantiated claims on Twitter on Saturday, alleging that “bad things” happened, referring to votes being “illegally received” and insisting he has won “by a lot”.

But Federal Election Commission commissioner Ellen Weintraub said there is no evidence of voter fraud.

Speaking on CNN after Mr Trump’s string of tweets – which were flagged by Twitter as containing information about the election that may be “misleading” – Ms Weintraub said: “State and local officials, and poll workers throughout the country, really stepped up.

“And there have been very few complaints about how this election has run.

“Very few substantiated complaints, let me put it that way. There is no evidence of any kind of voter fraud.”

“There is no evidence of illegal votes being cast.

“In fact, and you don’t have to take my word for it because people throughout the country, nonpartisan election experts have come out and hailed this election and how it was run.

“If you want to look at the state of Pennsylvania, which the president seems to be focused on, Senator (Pat) Toomey has come out and said he has seen no evidence of fraud there.

“The Republican leader of the state senate there has also said he has seen no evidence of fraud.”

She added: “There really has been no evidence of fraud. None of the complaints have attached any evidence of fraud.

“Really, we should feel very proud of ourselves.”

Her comments came after Mr Trump wrote on Twitter that tens of thousands of votes were “illegally received” after 8pn on Tuesday “totally and easily changing the results in Pennsylvania and certain other razor thin states”.

He said hundreds of thousands of Votes were “illegally not allowed to be OBSERVED”, adding: “This would ALSO change the Election result in numerous States, including Pennsylvania, which everyone thought was easily won on Election Night, only to see a massive lead disappear, without anyone being allowed to OBSERVE, for long intervals of time, what the happened…

“….Bad things took place during those hours where LEGAL TRANSPARENCY was viciously & crudely not allowed. Tractors blocked doors & windows were covered with thick cardboard so that observers could not see into the count rooms. BAD THINGS HAPPENED INSIDE. BIG CHANGES TOOK PLACE!”

Mr Trump said there will be a “big press conference” in Philadelphia on Saturday afternoon UK time, adding on Twitter: “I WON THIS ELECTION, BY A LOT!”

Twitter flagged this tweet, saying official sources may not have called the race when it was tweeted.

Meanwhile, Mr Biden has stopped short of officially declaring victory but said he is confident he is ultimately going to win the race to the White House.

The Democratic candidate took the lead in the key battleground states of Pennsylvania and Georgia on Friday, with forecasters putting him just one state from victory as officials continue counting votes.

Speaking in Wilmington, Delaware, just before 11pm on Friday local time, the former vice-president said although he did not have a final declaration “the numbers tell us a clear and convincing story”.

Mr Biden said: “We’re going to win this race, just look at what has happened since yesterday.”

He added: “We’ve gotten over 74 million votes, that’s more than any presidential ticket has ever gotten in the history of the United States of America.

“And our vote total is still growing. We’re beating Donald Trump by over four million votes and that’s a margin that’s still growing as well.”

Mr Biden finished his speech with an appeal for calm along with a veiled response to Mr Trump’s legal challenges, which the president has launched to improve his chances of re-election amid baseless allegations of fraud.

The winner needs to collect 270 electoral college votes by winning states.

Victory in Pennsylvania would hand the presidency to Mr Biden with its 20 votes but Georgia, with 16 electoral votes, is a more complicated scenario.

Not everyone agrees that Mr Biden has beyond all probability won in Arizona, and without that Georgia would leave him one vote short of overall victory.

He has secured victories in the battleground states of Wisconsin and Michigan but Nevada and North Carolina also remain too close to call after Tuesday’s election.

The Trump campaign requested a recount in Wisconsin and filed lawsuits in Pennsylvania, Michigan and Georgia.

But judges in Michigan and Georgia dismissed the actions launched by the Trump campaign.

Additional legal action was also expected in Nevada, the campaign indicated.

The Associated Press news agency, which PA relies on to call states, has projected Mr Biden as winning Arizona and its 11 electoral college votes.

That looks likely as he has a strong lead with more than 90% of the votes tallied – but Mr Trump’s campaign disagrees and other news organisations are not so certain.

The appearance of Mr Biden coming back from behind is an artificial one.

Many of the outstanding ballots are postal votes and absentee ballots that are being added to the tally later than their in-person counterparts.