After 21 days of refusing to concede the US election, Donald Trump has authorised the US government agency that must sign off on the presidential election to formally begin “initial protocols” that will recognise Joe Biden as the winner.

Mr Trump announced on Monday (local time) he was directing his team to co-operate on the transition “in the best interests of our country” but vowed to keep up the fight.

In a pair of tweets, he said he had recommended the little-known General Services Administration should “do what needs to be done with regard to initial protocols, and have told my team to do the same”.

Mr Trump has repeatedly falsely claimed he won the election and has spent weeks offering baseless claims of widespread voter fraud that have repeatedly failed to gain traction in the courts.

The dramatic move on Tuesday (Australian time) clears the way for the start of the transition from Mr Trump’s administration and allows Mr Biden to co-ordinate with federal agencies on plans for taking over on January 20.

Politicians and business executives have been pressuring the GSA to recognise the November 3 election results and free up millions of dollars in federal funds, office space and briefings for Mr Biden’s team.

An official said GSA administrator Emily Murphy – an appointee of Mr Trump – made the determination after the President’s efforts to subvert the vote failed across battleground states. His surprise move came just hours after Michigan certified Mr Biden’s victory there.

“I take this role seriously and, because of recent developments involving legal challenges and certifications of election results, am transmitting this letter today to make those resources and services available to you,” Ms Murphy wrote to Mr Biden.

“Contrary to media reports and insinuations, my decision was not made out of fear or favouritism.”

Tweet from @realDonaldTrump

Mr Trump tweeted shortly after her letter was made public: “Our case strongly continues, we will keep up the good … fight, and I believe we will prevail!”

“Nevertheless, in the best interest of our country, I am recommending that Emily and her team do what needs to be done with regard to initial protocols, and have told my team to do the same.”

Mr Biden welcomed the news.

“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,” his transition adviser Yohannes Abraham said, according to NBC News.

“This final decision is a definitive administrative action to formally begin the transition process with federal agencies.

“In the days ahead, transition officials will begin meeting with federal officials to discuss the pandemic response, have a full accounting of our national security interests, and gain complete understanding of the Trump administration’s efforts to hollow out government agencies.”

Mr Biden won the election with enough state-by-state electoral votes to secure the electoral college win. He leads the national popular vote by more than six million.

Mr Trump’s fellow Republicans have slowly broken from the President in recent days to urge the transition process to start.

-with AAP