Washington D.C. - After refusing for weeks to concede the election and work with Joe Biden on the smooth transfer of power, President Donald Trump has given the nod to a key federal agency to begin working with the incoming administration.

Trump (74), who falsely claims he won the election, tweeted on Monday evening that he was allowing the measure shortly after the General Services Administration (GSA) had contacted the Biden team to begin work to facilitate the transition of power.

The president vowed to continue the fight to overturn the election, an increasingly desperate and hopeless campaign. "I believe we will prevail," Trump said, but added that it was in the "best interest" of the country to allow a transition process to begin.

Biden's transition office confirmed the move. "This final decision is a definitive administrative action to formally begin the transition process with federal agencies," transition director Yohannes Abraham said in a statement.

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"Today's decision is a needed step to begin tackling the challenges facing our nation, including getting the pandemic under control and our economy back on track," Abraham said.

The GSA is a key administrative agency which will provide resources and other support to Biden as he shifts to taking office in January. Under US law, the outgoing administration must work with an incoming president's team to help ensure stability.

Trump has falsely claimed he won the election and is pursuing numerous court cases to try to stop Biden from being declared the winner.

Also on Monday, the Michigan State Board of Canvassers, the body in charge of making the state's election results official, certified the results of the election, with Biden winning the key swing state.

The move was the latest setback for the Trump campaign, which is suffering stinging defeats in courts, and effectively closes a last door to somehow fight the election outcome.

The legal team, which lost a key attorney over the weekend amid a barrage of unsubstantiated and increasingly bizarre claims, tried to ignore the Michigan outcome.

"Certification by state officials is simply a procedural step," said Jenna Ellis, a Trump legal adviser.