US President Donald Trump has intensified his attempts to cling to power amid conflicting reports about whether a witness who raised accusations of ballot tampering in Pennsylvania has recanted his allegations.

Mr Trump’s campaign earlier announced it will file a lawsuit to stop the battleground state of Michigan certifying election results.

The Michigan lawsuit will request election results in the state not be certified until it can be verified that votes were cast lawfully, Trump campaign attorney Matt Morgan said.

It was the latest in a string of lawsuits the Trump campaign has filed since Democrat Joe Biden captured the presidency.

Later in the day, Democrats on the House of Representatives Oversight Committee claimed postal worker Richard Hopkins had recanted his allegations, according to the Postal Service’s internal watchdog.

That office declined to comment.

The committee said on Twitter Mr Hopkins did not explain why he made up the allegations.

Tweet from @OversightDems

However, not long after, reports began emerging that Mr Hopkins was insisting he did not withdraw his allegations of ballot tampering.

Tweet from @realDonaldTrump

The Trump campaign had earlier provided Mr Hopkins’ affidavit to Republican Lindsey Graham, who then sent a letter to the Justice Department and the FBI requesting they launch an investigation.

The campaign filed suit on Monday (local time) in federal court in Pennsylvania to halt certification of that state’s results, alleging lax oversight of mail-in voting.

Latest in a series of Trump manoeuvres

Mr Biden’s victory in the November 3 election was propelled by wins in Michigan and Pennsylvania.

Mr Trump has repeatedly claimed, without evidence, that there was widespread voting fraud.

Judges have already tossed lawsuits in Michigan and Georgia brought by the campaign and legal experts say Mr Trump’s litigation has little chance of changing the election outcome.

Mr Trump’s accusations of fraud don’t appear to be gaining traction with the public either.

Nearly 80 per cent of Americans, including more than half of Republicans, recognise Mr Biden as the winner, according to a Reuters/Ipsos poll.

Top Republicans in Congress, including Senate Republican Leader Mitch McConnell, said Mr Trump had a right to challenge Mr Biden’s victory, and others echoed the President’s unfounded accusations of widespread fraud.

Privately, some aides said Mr Trump would need to produce credible evidence soon to retain their support.

Mr Biden secured more than the 270 votes in the Electoral College needed to take the presidency by winning Pennsylvania on Saturday after four tense days of counting delayed by a surge in mail-in ballots due to the coronavirus pandemic.

Mr Biden said in a speech in Delaware his team was pushing ahead with forming a new administration to take over on Inauguration Day, January 20, 2021, no matter what.

“We’re going to be going, moving along, in a consistent manner, putting together our administration, the White House, and reviewing who we’re going to pick for cabinet positions, and nothing’s going to stop that,” he said on Tuesday.

Mr Biden said it was an “embarrassment” that Trump has not conceded the election.

Mr Graham, a Trump ally, said on Saturday the Senate Judiciary Committee would investigate claims of irregularities in Pennsylvania after receiving an affidavit from a US Postal Service worker, who alleged illegal backdated postmarks may have been added to some late mail-in ballots.

Republicans in Pennsylvania urged an audit of the election results.

“We’ve just gotten a lot of allegations,” state Representative Dawn Keefer told reporters.

Trump attempts to strengthen power base

Mr Trump has continued installing loyalists in top positions at the Pentagon, one day after firing Defense Secretary Mark Esper, which could potentially make it easier to use US troops to respond to domestic protests.

Secretary of State Mike Pompeo earlier refused to acknowledge Mr Biden’s victory, claiming instead there will be “a smooth transition to a second Trump administration”.

The Biden transition team has been unable to move into federal office space or tap funds to hire staff because a Trump appointee who heads the federal office charged with recognising election results has not yet done so.

“The whole Republican Party has been put in a position with a few notable exceptions of being mildly intimidated by the sitting President,” said Mr Biden, who chuckled when asked about Mr Pompeo’s remarks.

British Prime Minister Boris Johnson, a conservative whose blustery style is often likened to Mr Trump’s, said he spoke to Mr Biden on Tuesday by phone about working together on priorities like climate change, promoting democracy and recovering from the pandemic.

Tweet from @Transition46

Mr Biden says nothing will stop the transfer of power in the US government as President Donald Trump pursues lawsuits in several states in a long-shot bid to hold on to power.

Bob Bauer, a senior Biden adviser, on Tuesday dismissed the Trump campaign’s litigation as “theatrics, not really lawsuits”.

-with agencies