A law firm representing President Donald Trump's campaign in challenging US election results in Pennsylvania is withdrawing from at least one of the cases contesting ballots in the battleground state.
Democrat Joe Biden was projected to have captured the presidency on Saturday, thanks in part to a win in Pennsylvania.
Mr Trump has refused to concede and has repeatedly alleged widespread voter fraud, for which there is still no evidence.
In a court filing on Thursday, lawyers at Porter Wright Morris & Arthur said it had agreed that its clients - the campaign and two registered voters - "will be best served if Porter Wright withdraws".
The campaign is in the process of retaining new counsel, Porter Wright said in the filing to US District Judge Matthew Brann in Williamsport, Pennsylvania.
The lawsuit, filed on Sunday in federal court in Pennsylvania, alleges that the state's mail-in voting system "lacked all of the hallmarks of transparency and verifiability that were present for in-person voters".
"We've committed to the court to fulfill our obligations as required to ensure transition to substitute counsel, and so as not to cause material adverse effect on the client's interest. We will have no further comment," Porter Wright said in a statement.
"The President's team is undeterred and will move forward with rock-solid attorneys to ensure free and fair elections for all Americans," Trump campaign spokesman Tim Murtaugh said in a statement on Friday.
Facing criticism over its work for the campaign from some Democrats and The Lincoln Project, a group of anti-Trump Republicans, Porter Wright said on Wednesday that it has a "long history" of bipartisan election work which "calls for us to take on controversial cases".
The Trump campaign has filed a flurry of lawsuits, part of a larger strategy to try to overturn the election results in key states.
