President Donald Trump pressured Georgia's top election official, a fellow Republican, in an extraordinary phone conversation to "find" enough votes to overturn Joe Biden's victory in the southern state, US media reported Sunday.

In the conversation with Secretary of State Brad Raffensperger on Saturday, a recording of which was first obtained by The Washington Post, Trump warns Raffensperger that he and his general counsel could face "a big risk" if they failed to pursue his request.

"The people of Georgia are angry, the people in the country are angry," Trump is heard saying on the tape, which was also aired by other media. "And there's nothing wrong with saying, you know, um, that you've recalculated," the president says. "You're off by hundreds of thousands of votes."

Raffensperger is heard responding: "Well, Mr President, the challenge that you have is, the data you have is wrong."

Biden won the traditionally conservative state by fewer than 12,000 votes -- a margin unchanged after recounts and audits. Even a hypothetical reversal there would not be enough to deprive Biden of victory.

Word of the recording came at an extraordinary juncture, two days before special runoff elections in Georgia that will decide control of the US Senate, and three days before Congress is to certify the results of the November 3 election.

That certification, normally routine, is now being challenged by scores of lawmakers at Trump's behest -- though Republican Congressman Adam Kinzinger urged them to reconsider in light of the tape. "This is absolutely appalling. To every member of Congress considering objecting to the election results, you cannot -- in light of this -- do so with a clean conscience," he tweeted.

'Contempt for democracy'

The New York Times reported that aides to Raffensperger had recorded the call, but that he told advisers he did not want it released unless the president attacked state officials or misrepresented what had been discussed.

On Sunday, before the audio was released, Trump tweeted about the call, saying that Raffensperger "was unwilling, or unable, to answer questions such as the 'ballots under table' scam, ballot destruction, out of state 'voters', dead voters, and more."

Raffensperger tweeted back, also ahead of the release of the audio, saying: "Respectfully, President Trump: What you're saying is not true. The truth will come out." After the audio was released, the White House declined to comment.

Democrats were quick to condemn the call. "Trump's contempt for democracy is laid bare. Once again. On tape," Representative Adam Schiff said on Twitter. "Pressuring an election official to 'find' the votes so he can win is potentially criminal, and another flagrant abuse of power by a corrupt man who would be a despot, if we allowed him. We will not."

Some political commentators compared the call to the Watergate tapes that led to the fall of past US president Richard Nixon.

Carl Bernstein, one of the reporters who helped bring down Nixon's presidency, called it "the ultimate smoking gun tape."

Trump has waged an all-out fight against the election results. But scores of recounts and lawsuits, as well as a review by his own Justice Department, have failed to substantiate the claims.

At one point, he invited Republican election officials from Michigan to the White House in an apparent effort to pressure them over their vote certification.

He also pressed Georgia Governor Brian Kemp, a Republican, in a separate phone call. Raffensperger and other election officials who have rejected Trump's entreaties, in Georgia and other states, have received death threats from his supporters.

Under Georgia law, Raffensperger can legally have taped the conversation without Trump's consent.