Georgia's top election official says Donald Trump pushed him to take an "inappropriate" call in which he pressured the state to overturn his November defeat there.
In the call on Saturday, Mr Trump told Georgia Secretary of State Brad Raffensperger , according to a recording published by US media.
"I never believed it was appropriate to speak to the president but he pushed out. I guess he had his staff push us; they wanted a call," Mr Raffensperger, who like Mr Trump is a Republican, told ABC's Good Morning America.
Two congressional Democrats have asked FBI Director Christopher Wray to investigate the call.
"We believe Donald Trump engaged in solicitation of, or conspiracy to commit, a number of election crimes. We ask you to open an immediate criminal investigation into the president," they said in a statement.
The Justice Department had no comment on the request by Representatives Ted Lieu and Kathleen Rice.
A state Democrat has called for a probe into whether Mr Trump had violated Georgia election law on the call.
Georgia Secretary of State Brad Raffensperger Source: ABACA
Mr Raffensperger and his office's general counsel rejected Mr Trump's assertions of electoral fraud in the hour-long conversation.
"We took the call and we had a conversation. He did most of the talking, we did most of the listening," Mr Raffensperger said.
"But I did want to make my points that the data that he has is just plain wrong. He had hundreds and hundreds of people he said that were dead that voted. We found two. That's an example of just he has bad data."
Mr Trump for two months has been claiming contrary to evidence that his loss to Mr Biden was the result of widespread fraud.
Multiple state and federal reviews, and courts have rejected this.
Mr Biden won the state-by-state Electoral College by 306-232 and carried the popular vote by more than 7 million ballots.
The only Democrat on Georgia's election board, David Worley, asked Mr Raffensperger in a letter on Sunday to investigate whether the president had violated state law that prohibits solicitation to commit election fraud.
Mr Raffensperger said the district attorney in Fulton County, home to Atlanta, might be the appropriate authority to carry out such an investigation.
The county's district attorney, Fani Willis, said she found news reports about Mr Trump's phone call with Mr Raffensperger "disturbing".
The state election board can refer the case to her office and the state attorney general, said Willis, a Democrat.
"I will enforce the law without fear or favour. Anyone who commits a felony violation of Georgia law in my jurisdiction will be held accountable," Ms Willis said.
In another blow to Mr Trump, staunch conservative Senator Tom Cotton refused to sign on to a long-shot campaign by some dozen other Republicans in the US Senate to challenge Mr Biden's victory.
Mr Cotton says he will not join colleagues Ted Cruz, Josh Hawley and others in defying Republican Party leaders by objecting on Wednesday when lawmakers meet to tally the votes in the Electoral College.
Mr Cotton, Mr Cruz and Mr Hawley are among those considered possible 2024 presidential candidates. Mr Trump, who has not conceded defeat, has also floated the idea of running in 2024.
Senate Republican leader Mitch McConnell has publicly acknowledged Mr Biden's win. Vice President Mike Pence, who will oversee Wednesday's proceedings, says Republicans have the right to object.
