President Donald Trump is to seek a partial recount of votes in the state of Wisconsin, which his rival Joe Biden is projected to win by 20,000 votes.
Hours before a Wednesday deadline, the Trump campaign said it wanted a recount in the counties of Milwaukee and Dane, alleging irregularities.
Mr Trump has been making claims of fraud and refusing to initiate a handover.
Mr Biden says delaying the transition will damage the US pandemic response.
The Trump campaign has filed a flurry of lawsuits contesting the results in key states, although election officials say there is no evidence of widespread irregularities.
Despite the lack of proof, up to half of Republican voters believe the president’s claim that the election was rigged against him.
President-elect Biden, a Democrat, is projected to have won the popular vote by more than 5.6 million ballots – 3.6 percentage points. In the US Electoral College system that decides the presidency, he has 306 votes to Mr Trump’s 232.
The president would have to overturn results in at least three states to win the election, which analysts say would be unprecedented.
A manual recount has been taking place in Georgia, where Mr Biden is 14,000 votes ahead. Results are expected to be released later today.