US President Donald Trump tweeted that “law enforcement is looking into another big corruption scandal having to do with Election Fraud in #Broward and Palm Beach”.
Senior Republicans have doubled down on claims by Donald Trump that Democrats were attempting to steal the razor-thin senatorial race in Florida, accusing both the incumbent and election officials of fraud.
The intensifying feud comes 18 years after the Sunshine State found itself at the heart of a battle for the US presidency, when George W. Bush prevailed over Al Gore after recounts were halted by the Supreme Court.
Republican Rick Scott, the state's governor until January when his term expires, launched into his rival Bill Nelson in his most direct terms to date Sunday, accusing him of orchestrating "fraud to try to win this election" as county officials scrambled to complete a recount by a Thursday deadline.
The theme was echoed by prominent Republican senators Lindsey Graham and Ted Cruz, escalating a campaign led by the president who said Saturday on Twitter: "Trying to STEAL two big elections in Florida! We are watching closely!"
Democrats for their part have accused Republicans of attempting to prevent votes from being counted, and pointed to the fact law enforcement has not found any evidence to substantiate rigging claims.
Nancy Pelosi, who is expected to be the Speaker of the House when the new Congress begins its term in January, hit back.
"There's no election fraud," she told CBS News, adding: "My experience with the president is, any time he charges somebody with something, he's just projecting what he might have done himself."
Florida produced some of the nation's closest results in Tuesday's midterm voting, including apparently narrow victories by Scott over Nelson and, in a gubernatorial race, by Republican Ron DeSantis over Democrat Andrew Gillum.
But with late-counted ballots narrowing Scott's lead to some 12,000 of the just over eight million votes cast -- an edge of less than half a percent - state law mandates a recount.
The governor's race has also gone to a recount and Gillum - in a move echoing Al Gore's withdrawal of his concession in 2000 amid electoral chaos in Florida - withdrew his concession.
But analysts say DeSantis's lead of nearly 34,000 votes will be tough for Gillum to overcome.
Scott had earlier accused Democratic election officials in two large counties of "rampant fraud," but speaking on "Fox News Sunday," he accused his rival by name.
"Senator Nelson is clearly trying to commit fraud to try to win this election," he said. "That's all this is."
Scott added: "Somehow they came up with 93,000 votes after election night. We still don't know how they came up with that."
That number apparently included many mail-in and provisional ballots, typically among the last counted.
Speaking on CBS, Graham denied Republicans had launched a campaign to undermine the integrity of the election.
"I think what undermines election integrity is Broward County can't get their act together," he said.
'Incompetence and mischief'
"The problem is not with President Trump's rhetoric, it is the incompetence and mischief of Broward County," he said.
Nelson's lawyers say local canvassing boards have wrongly rejected ballots when signatures did not precisely match those on record.
They said in a court filing that this led to the "disproportionate rejection of (mail-in) and provisional ballots cast by ethnic and racial minorities, as well as young, first-time voters."
Those groups tend to lean Democratic.
Scott has asked state law enforcement authorities to investigate.
Scott also accused Nelson's team of saying that a noncitizen should have the right to vote. But the single ballot in dispute was not counted, and Nelson's aides later said that was the correct decision.
In neighboring Georgia, Republican Brian Kemp, the secretary of state, holds a slim lead over Democrat Stacey Abrams. If late-arriving votes bring his total below 50 percent, a runoff will be held.
Counting meanwhile continues in Arizona in another tight US Senate race, with Democrat Kyrsten Sinema leading Republican Martha McSally by 1.3 percentage points but with thousands of votes remaining uncounted.
Trump on Friday tweeted: "Just out - in Arizona, SIGNATURES DON'T MATCH. Electoral corruption - Call for a new Election? We must protect our Democracy!"
But outgoing senator Jeff Flake of Arizona, a fellow Republican but sometime Trump critic, tweeted, "There is no evidence of 'electoral corruption' in Arizona, Mr. President."
As things stand, Republicans have added a few seats to their 51-49 edge in the US Senate, while Democrats have taken clear control of the House of Representatives, picking up more than 30 seats.