Donald Trump's campaign has branded the chaotic Democratic caucus in Iowa "the sloppiest train wreck in history".
Details of the results from the party's gathering were delayed indefinitely due to "quality checks" after voting ended on Monday.
Seizing on the delays, Trump campaign manager Brad Parscale said: "Democrats are stewing in a caucus mess of their own creation with the sloppiest train wreck in history.
"It would be natural for people to doubt the fairness of the process. And these are the people who want to run our entire health care system?"
The results were postponed after voters gathered in more than 1,600 sites across Iowa, for the first such gatherings in the states.
Those in attendance have been the first to officially outline who they wish to take on President Trump in the election later this year.
They voted on 11 Democratic contenders led by front-runners Bernie Sanders and former vice president Joe Biden.
The Democrat's state party in Iowa said it was working to verify the results and had found "inconsistencies in the reporting" of date from caucus sites.
State party spokeswoman Mandy McClure said: "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 results are being hand-checked, according to The Washington Post.
Those involve in the Democratic campaigns have been told they will receive the results later on Tuesday, the paper added.
