President-elect Joe Biden has been recognised as the "apparent winner" of the US election, formally starting the transition of power after President Donald Trump spent weeks testing the boundaries of American democracy.
General Services Administrator Emily Murphy gave the green light on Monday for Biden to coordinate with federal agencies ahead of his January 20 inauguration.
The move came after Trump suffered yet more legal and procedural defeats in his seemingly futile effort to overturn the election with baseless claims of fraud.
Trump still refused to concede, but tweeted that he was directing his team to cooperate on the transition.
Murphy, explaining her decision, cited "recent developments involving legal challenges and certifications of election results."
She acted after Michigan on Monday certified Biden's victory in the battleground state, and a federal judge in Pennsylvania tossed a Trump campaign lawsuit on Saturday seeking to prevent certification in that state.
It also came as an increasing number of Republicans were publicly acknowledging Biden's victory, after weeks of tolerating Trump's baseless claims of fraud. The president had grown increasingly frustrated with the flailing tactics of his legal team.
In recent days, senior Trump aides including chief of staff Mark Meadows and White House counsel Pat Cipollone had encouraged him to allow the transition to begin, telling the president he didn't need to concede but could no longer justify withholding support to the Biden transition.
Yohannes Abraham, executive director of the Biden transition, said the 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."
Murphy, a Trump appointee, had faced bipartisan criticism for failing to begin the transition process sooner, preventing Biden's team from working with career agency officials on plans for his administration. The delay denied Biden access to highly classified national security briefings and hindered his team's ability to begin drawing up its own plans to respond to the raging coronavirus pandemic.
Murphy insisted she acted on her own.
"Please know that I came to my decision independently, based on the law and available facts. I was never directly or indirectly pressured by any Executive Branch official - including those who work at the White House or GSA - with regard to the substance or timing of my decision," she wrote in a letter to Biden.
Trump tweeted moments after Murphy's decision: "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."
Max Stier, president and CEO of the nonpartisan Partnership for Public Service, criticised the delay but said Biden's team would be able to overcome it.
"Unfortunately, every day lost to the delayed ascertainment was a missed opportunity for the outgoing administration to help President-elect Joe Biden prepare to meet our country's greatest challenges," he said. "The good news is that the president-elect and his team are the most prepared and best equipped of any incoming administration in recent memory."
Senate Democratic leader Chuck Schumer said the GSA action "is probably the closest thing to a concession that President Trump could issue. Noting that the nation "faces multiple crises that demand an orderly transition " Schumer urged Democrats and Republicans to unite for a smooth and peaceful transition that will benefit America.
Australian Associated Press