The US presidential election on November 3 was "the most secure in American history", the US body charged with election oversight has said, directly repudiating Donald Trump's repeated baseless claims of widespread fraud.
A Department of Homeland Security (DHS) cybersecurity unit says it has no evidence that votes were compromised or altered in last week's vote, which has seen Joe Biden declared as the winner.
The outgoing president has refused to concede the election or recognise President-Elect Biden as the victor, and has launched legal action in several key states.
“The November 3rd election was the most secure in American history. Right now, across the country, election officials are reviewing and double checking the entire election process prior to finalizing the result," says the statement from the Cybersecurity and Infrastructure Security Agency (CISA).
"There is no evidence that any voting system deleted or lost votes, changed votes, or was in any way compromised," it adds. Trump tweeted on Thursday an unfounded claim that voting software had erased millions of votes for him.
The statement's authors include the presidents of federal and state election bodies. It echoes repeated assertions by election experts and state officials over the last week that the election unfolded smoothly without broad irregularities.
The statement concludes by saying that despite the "many unfounded claims and opportunities for misinformation", the American public can have "the utmost confidence in the security and integrity of our elections".
"We have confidence in the security of your vote, you should, too," tweeted CISA's director Chris Krebs.
The message is in stark contrast to Trump's unsupported claims of fraud and widespread problems that he insists could affect vote totals.
It is unclear whether his refusal to acknowledge Joe Biden's victory is childish petulance, an attempt to muddy the waters over the election process and fire up his base, an effort to secure funding for future campaigns, part of a serious attempt to mount some kind of political or constitutional coup to overturn the result -- or a combination of some or all of these factors.
Although voting continues in some states, most ballots have been tallied and Biden is widely projected to have passed the 270 electoral college votes needed to secure the White House.
The issues Trump’s campaign and its allies have pointed to are typical in every election: problems with signatures, secrecy envelopes and postmarks on mail-in ballots, as well as the potential for a small number of ballots miscast or lost. With Democrat Joe Biden leading Trump by wide margins in key battleground states, none of those issues would have any impact on the outcome of the election.
Former President Barack Obama has hit out at senior Republicans for playing along with Donald Trump's baseless claims of fraud, saying they should "know better" and accusing them of going down a "dangerous path" of helping to de-legitimise democracy.
A small number of Republicans have distanced themselves from the outgoing president's stance, backing calls for Joe Biden to be given access to US security briefings and accepting there should be moves towards a smooth transition of power. But the majority have not acknowledged the president-elect's victory.