Donald Trump has accepted a formal US transition should begin for President-elect Joe Biden to take office.

The president said the federal agency overseeing the handover must "do what needs to be done", even as he vowed to keep contesting his election defeat.

The General Services Administration (GSA) said it was acknowledging Mr Biden as the "apparent winner".

It came as Mr Biden's victory in the state of Michigan was officially certified, a major blow to Mr Trump.

"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," a team statement said.

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

After the GSA announcement, the Pentagon said it would provide "support to the Biden team... in a professional, orderly, and efficient manner that is befitting of the public's expectation of the Department and our commitment to national security".