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.
Joe Biden through the years
Joe Biden through the years
Washington, DC. 6-9-1987 Senator Joe Biden (D.,DE.) announces his candidacy for president. Credit: Mark Reinstein (Photo by Mark Reinstein/Corbis via Getty Images)
Sens. Joe Biden, D-Del., and Strom Thurmond, R-S.C. September 9, 1990 (Photo by Maureen Keating/CQ Roll Call via Getty Images)
Democratic politician Joseph R. Biden Jr, the United States Senator from Delaware, circa 1980. He became the US Vice President in 2009 under President Barack Obama. (Photo by Nancy Shia/Archive Photos/Getty Images)
American politician and US Senator (and future US Vice President) Joe Biden smiles in a 'Bicentennial Minutes' segment, a series of nightly shorts commemorating the bicentennial of the American Revolution which aired from 1974-1976, August 12, 1974. (Photo by CBS Photo Archive/Getty Images)
WASHINGTON, : US Senator Joe Biden(D-DE) briefs reporters prior to the 15 January start of the second day of the US Senate impeachment trial of US President Bill Clinton on Capitol Hill in Washington, DC. House prosecutors will summarize their case against the president 15 January. (ELECTRONIC IMAGE) AFP PHOTO/Luke FRAZZA (Photo credit should read LUKE FRAZZA/AFP/Getty Images)
392389 02: U.S. President George W. Bush meets with members of the Senate and House foreign policy leadership in the Cabinet room at the White House July 25, 2001 in Washington, DC. Seated next to the president is Sen. Joe Biden (D-DE). (Photo by Mark Wilson/Getty Images)
UNITED STATES - MARCH 08: Joe Biden during the 2004 Democratic National Convention in Boston, Massachusetts. (Photo By Douglas Graham/Roll Call/Getty Images)
UNITED STATES - MAY 12: Democrat vice chairman of the Senate Foreign Relations Committee Senator Joe Biden (D-DE), throws up his hands as he speaks during debate on the nomination of John Bolton as US Ambassador the the United Nations May 12, 2005 in Washington D.C. (Photo by Joe Marquette/Bloomberg via Getty Images)
WASHINGTON - JULY 12: U.S. Senator Joseph Biden (D-DE) speaks during the Senate Foreign Relations Committee hearing on 'North American Cooperation on the Border' on the Border' on Capitol Hill July 12, 2005 in Washington, DC. The committee discussed border security and how to work together to secure the borders with Mexico and Canada. (Photo by Joe Raedle/Getty Images)
THE TONIGHT SHOW WITH JAY LENO -- Episode 3331 -- Pictured: (l-r) Senator Joe Biden during an interview with host Jay Leno on March 22, 2007 (Photo by Paul Drinkwater/NBC/NBCU Photo Bank via Getty Images)
ORANGEBURG, SC - APRIL 26: (L-R) U.S. Sen. Joe Biden (D-DE) and New Mexico Gov. Bill Richardson greet the crowd before the start of the first debate of the 2008 presidential campaign April 26, 2007 at South Carolina State University in Orangeburg, South Carolina. The debate, featuring eight Democratic presidential candidates, comes 263 days before the first ballot will be cast in the Iowa caucus next January. (Photo by Justin Sullivan/Getty Images)
WASHINGTON, DC - JANUARY 23: U.S. Vice President Joe Biden (C) talks with mayors from across the country, including Milwaukee Mayor Tom Barrett, in the Roosevelt Room of teh White January 23, 2014 in Washington, DC. The U.S. Conference of Mayors is holding its annual conference in Washington this week. (Photo by Chip Somodevilla/Getty Images)
US Vice President Joe Biden speaks during the Civil Society Forum on the sideline of the US-Africa Leaders Summit in Washington, DC, on August 4, 2014. Washington aims to wake up US business to the opportunities in Africa with the landmark US-Africa Leaders Summit this week, as China and Europe steal a march on the world's fastest-growing continent. As many as four dozen African leaders, and hundreds of businessmen with them, will for their part be looking to see if US investors and traders can move beyond old stereotypes of a continent mired in conflict and corruption and recognize its huge potential. AFP PHOTO/Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
WASHINGTON, DC - AUGUST 18: U.S. Vice President Joe Biden (R) swears in Secretary of Housing and Urban Development Julian Castro (L) as his wife Erica and daughter Carina look on during a ceremonial swearing in ceremony in the Eisenhower Executive Office Building August 18, 2014 in Washington, DC. Castro, the former Mayor of San Antonio, Texas, was officially sworn in on July 28. (Photo by Win McNamee/Getty Images)
WASHINGTON, DC - JUNE 30: (AFP OUT) U.S. President Barack Obama (C), Robert McDonald (R) and Vice President Joe Biden walk back to the White House through LaFayette Park after President Obama announced his intention to nominate Robert McDonald to lead the Department of Veterans Affairs June 30, 2014 in Washington, DC. McDonald served as the chief executive of Procter & Gamble and will replace Eric Shinseki who resigned after allegations of delayed care came to light. (Photo by Dennis Brack-Pool/Getty Images)
US President Barack Obama speaks to US Vice President Joe Biden after Biden introduced him during a signing ceremony for H.R. 803, the Workforce Innovation and Opportunity Act, on July 22, 2014 in the South Court Auditorium of the Eisenhower Executive Office Building, next to the White House in Washington, DC. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)
US Presidential Barack Obama speaks on immigration reform beside US Vice President Joe Biden (R) in the Rose Garden of the White House on June 30, 2014 in Washington, DC. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)
COLORADO SPRINGS, CO - MAY 28: Vice President of the United States Joe Biden takes a selfie after the commencement ceremony at Air Force Academy in Colorado Spring, May 28, 2014. Biden spoke during the ceremony. (Photo by RJ Sangosti/The Denver Post via Getty Images)
US Vice President Joe Biden gestures as he speaks at Ledra palace in the UN-patrolled Buffer Zone in Nicosia on May 22, 2014. Biden met Cyprus leaders Thursday to spur talks on ending the island's 40-year division and seek support for threatened sanctions against Russia despite the economic cost. AFP PHOTO/ ANDREW CABALLERO-REYNOLDS (Photo credit should read Andrew Caballero-Reynolds/AFP/Getty Images)
US Vice President Joe Biden adresses a speech to students and officials at Cotroceni Palace, the Romanian Presidency headquarters in Bucharest on May 21, 2014. Tougher sanctions must be imposed on Russia if it undermines crucial presidential elections in Ukraine on May 25, 2014, US Vice President Joe Biden said in Bucharest. AFP PHOTO DANIEL MIHAILESCU (Photo credit should read DANIEL MIHAILESCU/AFP/Getty Images)
WASHINGTON, DC - APRIL 29: U.S Vice President Joe Biden speaks during an event on protecting students from sexual assault at the Eisenhower Executive Office Building April 29, 2014 in Washington, DC. During the event, Biden announced the release of the first report of the White House Task Force to Protect Students from Sexual Assault. (Photo by Win McNamee/Getty Images)
US Vice President Joe Biden (L) and outgoing Heath and Human Services Secretary Kathleen Sebelius applaud as President Barack Obama names Sylvia Mathews Burwell (R), his current budget director, to replace Sebelius in the Rose Garden at the White House in Washington,DC on April 11, 2014. Sebelius resigned, paying the price for the chaotic initial rollout of the US president's signature health care law. AFP PHOTO/Nicholas KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images)
US Vice President Joe Biden waves upon arrival for a meeting with Lithuania's President in Vilnius on March 19, 2014. Biden meets today with Lithuanian President Dalia Grybauskaite and Latvian leader as part of a tour to reassure NATO allies during the Ukraine crisis. AFP PHOTO / PETRAS MALUKAS (Photo credit should read PETRAS MALUKAS/AFP/Getty Images)
US Vice President Joe Biden listens during a meeting with the Polish Prime Minister in Warsaw, Poland on March 18, 2013. Biden arrived in Poland for talks with regional allies as Russia tightened its grip on the Ukraine's breakaway region of Crimea. AFP PHOTO / JANEK SKARZYNSKI (Photo credit should read JANEK SKARZYNSKI/AFP/Getty Images)
US Vice President Joe Biden arrives for a St. Patrick's Day reception in the East Room of the White House on March 14, 2014 in Washington. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)
US Vice President Joe Biden during a joint press conference with Chile's President Sebastian Pinera (not framed) at La Moneda presidential palace in Santiago, on March 10, 2014. AFP PHOTO/CLAUDIO REYES (Photo credit should read Claudio Reyes/AFP/Getty Images)
WASHINGTON, DC - FEBRUARY 27: U.S. Vice President Joe Biden delivers remarks during the Democratic National Committee's Winter Meeting at the Capitol Hilton February 27, 2014 in Washington, DC. Biden addressed the Association of State Democratic Chairs. (Photo by Chip Somodevilla/Getty Images)
THE VIEW - Joe Biden, the 47th Vice President of the United States, was the special guest, live, TUESDAY, FEBRUARY 25 (11:00 a.m.-12:00 noon, ET). The Vice President discussed the Affordable Care Act and the importance of signing up for health insurance through the marketplace before the March 31 deadline. Vice President Biden sat down with The View hosts Barbara Walters, Whoopi Goldberg, Sherri Shepherd and Jenny McCarthy as part of the shows continuing Red, White & View campaign, which is committed to political guests and discussions. 'The View' airs Monday-Friday (11:00 am-12:00 pm, ET) on the ABC Television Network.
(Photo by Lou Rocco/ABC via Getty Images)
SHERRI SHEPHERD, BARBARA WALTERS, VICE PRESIDENT JOE BIDEN, WHOOPI GOLDBERG, JENNY MCCARTHY
U.S. Vice President Joe Biden, left, looks on as President Barack Obama speaks at the White House in Washington, D.C., U.S., on Friday, Jan. 31, 2014. Obama is meeting today with chief executive officers of companies from Bank of America Corp. to EBay Inc. who have committed to giving the long-term unemployed a better chance in the hiring process. Photographer: Joshua Roberts/Bloomberg via Getty Images *** Barack Obama; Joe Biden
US Vice President Joe Biden gives two thumbs-up prior to US President Barack Obama delivering the State of the Union address before a joint session of Congress on January 28, 2014 at the US Capitol in Washington. AFP PHOTO/Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)
CAMBRIDGE, MA - MAY 24: Former Vice President Joseph Biden speaks at the Harvard College Class of 2017 Class Day Exercises at Harvard University on May 24, 2017 in Cambridge, Massachusetts. Biden implored graduating students to become involved and paraphrased Plato by saying 'The penalty you pay for not being involved is that you are governed by those worse than you.' (Photo by Paul Marotta/Getty Images)
CAMBRIDGE, MA - MAY 24: Former Vice President Joe Biden jokes, 'Let's break the internet' as he puts on a pair of shades during Class Day Exercises at Harvard University in Cambridge, Mass., on May 24, 2017. (Photo by Jessica Rinaldi/The Boston Globe via Getty Images)
Former U.S. Vice President Joe Biden, left, and Michael Milken, chairman of the Milken Institute, arrive on stage at the Milken Institute Global Conference in Beverly Hills, California, U.S., on Wednesday, May 3, 2017. The conference is a unique setting that convenes individuals with the capital, power and influence to move the world forward meet face-to-face with those whose expertise and creativity are reinventing industry, philanthropy and media. Photographer: David Paul Morris/Bloomberg via Getty Images
WASHINGTON, DC -ï¿½ APRIL 26: Former Vice President, Joe Biden and Mark Ein are seen at the game between the Washington Wizards and the Atlanta Hawks in Game Five of the Eastern Conference Quarterfinals of the 2017 NBA Playoffs on April 26, 2017 at Verizon Center in Washington, DC. NOTE TO USER: User expressly acknowledges and agrees that, by downloading and or using this Photograph, user is consenting to the terms and conditions of the Getty Images License Agreement. Mandatory Copyright Notice: Copyright 2017 NBAE (Photo by Scott Cunningham/NBAE via Getty Images)
Joe Biden, former Vice President of the US tours the Museum of the American Revolution, on its openings day, in Philadelphia, PA, on April 19, 2017. (Photo by Bastiaan Slabbers/NurPhoto via Getty Images)
WASHINGTON, DC - JANUARY 12: (AFP OUT) U.S. President Barack Obama (R) presents the Medal of Freedom to Vice-President Joe Biden during an event in the State Dinning room of the White House, January 12, 2017 in Washington, DC. (Photo by Olivier Douliery-Pool/Getty Images)
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"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.