Results from Iowa's caucuses, the first vote in the race to pick a Democratic White House candidate to face President Donald Trump, have been plunged into chaos by apparent technology issues.
The state's Democratic party said it had found "inconsistencies".
But they stressed the unprecedented holdup was a "reporting issue", not a "hack or an intrusion".
Voters flocked to over 1,600 schools, libraries and churches across 99 counties on Monday to pick candidates.
The candidates are vying to win the opening contest of the 2020 White House campaign and become the Democratic nominee who will challenge Mr Trump, a Republican, in the 3 November election.
The front-runners among the 11 remaining contenders are Vermont Senator Bernie Sanders, former US Vice-President Joe Biden, Pete Buttigieg, the former mayor of South Bend, Indiana, Massachusetts Senator Elizabeth Warren and Minnesota Senator Amy Klobuchar.
Amid the delay, party officials held a call with the rival campaigns.
Iowa Democratic Party spokeswoman Mandy McClure said: "We found inconsistencies in the reporting of three sets of results. In addition to the tech systems being used to tabulate results, we are also using photos of results and a paper trail to validate that all results match and ensure that we have confidence and accuracy in the numbers we report.
"This is simply a reporting issue, the app did not go down and this is not a hack or an intrusion. The underlying data and paper trail is sound and will simply take time to further report the results."
A muddled mess
The Democratic Party establishment spent the past few days hand-wringing over what they might view as a doomsday scenario where outsider Bernie Sanders posted a solid win in the Iowa caucuses. It turns out they're heading towards an outcome much worse than that.
Three years after having their party servers hacked by Russians in an attempt to disrupt the 2016 election, a "quality control issue" derailed the reporting of the Iowa results.
It's not a good look for the Democratic Party – or for American democracy.
It will be a snafu that launches 1,000 conspiracy theories and leaves a race that might have received some clarity after a year of campaigning a muddled mess as the primary season gets underway.
What went wrong?
But her statement was flatly contradicted by party officials at county level, who blamed technology issues for the delay.
They said an app created for caucus organisers to report their results had malfunctioned, leaving precinct officials to call in the outcome to state party headquarters, whose phone lines swiftly became jammed.
Elesha Gayman, the Democratic chairwoman of Scott county, Iowa's third largest, said many of her precinct captains were having issues reporting results.
She said they had been on hold for a long time and she knew of only one precinct captain who had been able to report via the app.
Dallas County chairman Bryce Smith also said the app had crashed.
Nate Gruber, the Democratic vice-chairman of Black Hawk county, a part of the state with the largest concentration of African Americans, said he had not been able to use the app eithRead More – Source
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