Washington D.C. - Vice President-elect Kamala Harris described outgoing president Donald Trump's efforts to have election results in the state of Georgia overturned, a "bald-faced, bold abuse of power".

In his latest effort to challenge results of the presidential election he lost to Joe Biden (78), Trump – in an hour-long Saturday phone call – pressured Georgia's top elections official to "find" nearly 12,000 votes needed to flip the state in his favor, according to recordings published on Sunday by the Washington Post.

Trump's actions reveal "the voice of desperation," Democrat Harris said Sunday night at a campaign appearance in Savannah, Georgia.

Georgia Secretary of State Brad Raffensperger, a fellow Republican, dismissed the president's claims in the call, telling Trump they were based on debunked conspiracy theories.

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"He has no clue!" Trump (74) tweeted about Raffensperger on Sunday, saying he had phoned the secretary of state about "voter fraud in Georgia."

Georgia will hold runoff elections Tuesday for two Senate seats, the results of which could tip the Republican majority in the chamber.

Trump and Biden planned to campaign again in person in Georgia on Monday.

Meanwhile, the new US Congress convened for the first time on Sunday amid threats by Republican senators to vote against the upcoming certification of presidential election results.

The House of Representatives met at noon, as prescribed in the Constitution, and then voted to elect a new speaker. Nancy Pelosi was re-elected to the role by a narrow margin.

The 80-year-old California Democrat, the only woman to have ever served as speaker, has led the House Democrats for 17 years. It is expected to be her last term in the House's top job.

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However, Pelosi faces challenges in the 117th Congress, leading the narrowest majority in two decades in the lower chamber after Democrats lost seats in the November election.

Control of the Senate is still undetermined and will be decided by two hotly-contested run-off elections in Georgia on Tuesday.

Newly elected and returning members of Congress were being sworn in in small groups at the US Capitol as a safety precaution amid the still-raging coronavirus pandemic, which also forced festivities to be cancelled.

Vice President Mike Pence (61) elbow bumped senators after administering the oath of office to them.

"To say the 117th Congress convenes at a challenging time would indeed be an understatement," Senate Majority Leader Mitch McConnell (78) said as he welcomed senators.

"From political division to a deadly pandemic to adversaries around the world, the hurdles before us are many and they are serious," he said, adding there were also "reasons for hope."

Congress will face its first major test on Wednesday when it is mandated to certify president-elect Joe Biden's election victory before his inauguration on January 20.

The normally routine occasion risks being complicated by a group of Republican lawmakers who have said they will vote against the certification of electors from US states where President Donald Trump has disputed Biden's win.

The move to subvert the vote is widely expected to fail and simply draw out the certification process. It is also creating a rift in the Republican party.

A day after 11 Republican senators said they intended to appeal the certification, a bipartisan group of 10 senators on Sunday issued a statement urging their colleagues to support the electoral college vote. "The 2020 election is over," they said.

Trump has been promoting unfounded claims that the election was rigged against him, but has provided no proof that swayed any court to his side.