A former presidential candidate looks likely to spur a last-minute recount of part of the result of the US election.
Donald Trump narrowly beat Hillary Clinton in Wisconsin, but two voting rights experts say the result needs to be more closely analysed.
Green Party presidential candidate Jill Stein says she has gathered enough money to fund a recount in Wisconsin.
There is no indication Mr Trump's win was down to cyberhacking, one of the experts said on Wednesday.
One election official in Wisconsin said they are preparing for a possible recount.
What are the concerns?
On Tuesday, New York magazine first reported that a group of experts, led by voting-rights lawyer John Bonifaz and J Alex Halderman, the director of the University of Michigan Center for Computer Security and Society, had contacted Mrs Clinton's campaign.
The experts urged her campaign to request recounts in two states narrowly won by Mr Trump - Wisconsin and Pennsylvania - as well as Michigan, where he has a small lead.
In a post on Medium on Wednesday, Mr Halderman repeated concerns he has voiced in the past over the vulnerabilities of paperless voting machines.
The fact that the results in the three states was different from what polls predicted was "probably not" down to hacking, Mr Halderman said. Concerns over possible Russian interference were expressed in the run-up to the vote.
"The only way to know whether a cyberattack changed the result is to closely examine the available physical evidence ," he wrote.
Read more: Fears of a Russian hack
Why the urgency?
There is a deadline for any candidates to demand a recount, and they need to pay fees to file a request.
The deadline for Wisconsin is Friday. Pennsylvania's is Monday, and Michigan's is Wednesday.
This is where Jill Stein comes in - on her website, she wrote that recounts were needed "to attempt to shine a light on just how untrustworthy the US election system is".
By late on Wednesday, she had raised, through a crowdfunding campaign, more than $2.5m (£2m), enough to fund a recount request in Wisconsin. The campaign estimates that up to $7m may be needed to pay for recounts in all three states.
What happened in Wisconsin?
Unofficial results from the state showed Mr Trump won by only 27,000 votes, media in the state say. The BBC's results show he won 47.9% of the vote, with 46.9% going to Mrs Clinton (Jill Stein won only 1% of the votes there).
Before then, the state had gone with the Democrats for seven elections running.
A Clinton victory in Wisconsin alone would not have been enough to overturn Mr Trump's lead - it provides only 10 votes in the crucial electoral college that gave him victory. But wins in Wisconsin, Michigan and Pennsylvania would have clinched the presidency for the Democrat.
The Wisconsin State Journal quoted the state's election commission director Michael Haas as saying that the organisation had not seen "any reason to suspect that any voting equipment has been tampered with".
The commission was now preparing for a recount, Mr Haas told the newspaper, that added that such a move would be "unprecedented".
Read more: How did Clinton get more votes and lose?
What have the other candidates said?
There has been no official comment from Mr Trump's camp, and while supporters of Mrs Clinton have been taking to social media with the hashtag #AuditTheVote, there has been no formal request for a recount on her side, or the party's.