Joe Biden said Wednesday that Americans "won't stand" for attempts to derail the U.S. election outcome, but Donald Trump doubled down on his unprecedented refusal to concede defeat and called for the results to be overturned. 

In a speech on the eve of the Thanksgiving holiday, Biden said in his hometown Delaware that Americans "have full and fair and free elections, and then we honor the results." "The people of this nation and the laws of the land won't stand for anything else," he said. 

The Democrat's statement signaled a hardening line against Trump who for more than three weeks has been touting conspiracy theories, with no meaningful evidence, that Biden stole victory on November 3. 

Trump dug his heels in, though. "We have to turn the election over," he told Republican supporters in Pennsylvania. 

"This election was rigged," Trump said via telephone, repeating several claims of vote tampering that have been shot down in courtrooms across the country. Trump said "all we need is to have some judge listen to it properly". 

Trump had been due earlier to appear in person at the Republican meeting, which took place near the Civil War battlefield site of Gettysburg. He cancelled at the last minute. 

The gathering, which also featured Trump's controversial personal lawyer Rudy Giuliani, was falsely portrayed by the president on Twitter as a "very important Pennsylvania State Senate hearing." It was in fact held in a hotel in the small town and, rather than an official hearing, was merely a forum for Trump's ardent supporters to push his evidence-free claims.  

Biden won Pennsylvania by a margin of 80,000 votes on November 3, helping him assemble a convincing nationwide victory and making Trump a one-term president. 

Meanwhile, the U.S. State Department has informed staff that the transition process has begun and a team had been assigned inside the agency to support a handover to the incoming Biden administration, according to an internal email seen by Reuters on Wednesday. 

The guidelines, sent on Wednesday, came after the General Services Administration (GSA), the federal agency that must sign off on presidential transitions, notified Biden on Monday that he could formally begin the transition process. 

(With input from AFP and Reuters; cover via Reuters)