There is no evidence of compromised ballots or corrupt voting systems in the United States election, officials said on Thursday, as a top Democrat accused Republicans who refuse to accept President-elect Joe Biden's win of “poisoning” democracy.

Their messages came hours after President Donald Trump once again cried foul, tweeting a baseless claim that an election equipment maker “deleted” 2.7 million votes for him nationwide.

Biden, who leads by more than five million in the popular vote, cemented his victory late on Thursday by winning Arizona, US networks said, flipping the state Democratic for the first time since 1996.

Arizona gives Biden a 290-217 lead over Trump in the Electoral College, with 270 needed to win the White House.

With most Republican lawmakers having yet to acknowledge Biden's win, Senate Minority Leader Chuck Schumer, the chamber's top Democrat, accused them on Thursday of “denying reality” and “auditioning for profiles in cowardice".

“Instead of working to pull the country back together so that we can fight our common enemy Covid-19, Republicans in Congress are spreading conspiracy theories, denying reality and poisoning the well of our democracy,” he said.

Senior US federal and state election officials, meanwhile, in a statement rejected Trump's claims of fraud, saying that “the November 3rd election was the most secure in American history". The statement was issued by the Election Infrastructure Government Coordinating Council, a public-private umbrella group under the primary federal election security body, 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,” they said.

“While we know there are many unfounded claims and opportunities for misinformation about the process of our elections, we can assure you we have the utmost confidence in the security and integrity of our elections, and you should too,” the statement said.

It was signed by the heads of the National Association of State Election Directors and the National Association of Secretaries of State — the officials who manage elections at the state level — and by the chairman of the US Election Assistance Commission.

'Absurd circus'

The statement came just hours after Trump's tweet, which in addition to claiming 2.7 million “deleted” votes also said hundreds of thousands had been switched from him to Biden in Pennsylvania and other states.

It was the latest in a series of bogus assertions Trump and Republicans have put forth in order to reject Biden's victory.

Republican lawmakers such as Senate Majority Leader Mitch McConnell have stood firm with Trump by supporting his refusal to concede and backing his legal challenges.

Democratic House Speaker Nancy Pelosi weighed in on Thursday to demand Republicans stop what she called an “absurd circus” and turn to combatting the pandemic.

“Now that the people have expressed their views, Joe Biden has won (and) Kamala Harris will be the first woman vice president of the United States,” Pelosi said.

Political experts believe Republicans may be invoking such a strategy as a way to rile up Trump's base before two US Senate runoff elections in Georgia that will determine which party controls the chamber.

A total of 161 former national security officials, including some who worked with Trump, additionally warned the current administration's continued delay in recognising Biden's victory is posing “a serious risk to national security".

In a letter, the group including ex-Pentagon chief Chuck Hagel and Trump's former National Security Council senior counterterrorism director Javed Ali urged General Services Administration (GSA) chief Emily Murphy to recognise Biden as the apparent president-elect.

Without a GSA signoff, transition funds and other resources including access to intelligence briefings cannot flow to Biden and his team, but Murphy has refused to budge.