NEW YORK/WASHINGTON (Reuters) - Democratic National Committee officials on Friday rejected plans to let people participate in Iowa’s and Nevada’s early caucuses by phone because of security concerns, drawing fire from at least one candidate for leaving voters out of the party’s presidential contest.

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Each U.S. state party hosts nominating contests ahead of the 2020 election. Iowa’s caucus is the first in the nation, on Feb. 3, and Nevada’s follows later that month.

Unlike a primary election, Democrats at the caucus gather in groups to show their support for candidates. The events are lengthy and held in winter, making it difficult for people to attend, so both states had introduced plans to let some voters participate over the phone in a “virtual caucus.”

There were signs those systems could be hacked. On Friday, DNC Chair Tom Perez and other officials said no telephone caucus technology “meets our standard of security and reliability,” and said they would recommended not using those systems in Iowa and Nevada.

"The DNC needs to get its act together so that it doesn't disenfranchise tens of thousands of Iowans," said Julian Castro, a Democratic presidential candidate and former federal housing chief, in a video here posted online. "They either need to make sure that they figure out a secure virtual caucus process or, alternatively, allow another form of absentee voting."

The Democratic party has told states either to hold primaries or to allow more participation in their caucuses. Consequently, several states abandoned their caucuses to hold primaries. If Iowa switched to a primary, it could lose its status as the earliest nominating contest. The Des Moines Register reported first that the DNC would block Iowa’s virtual caucus plan.

The Iowa Democratic Party said in a statement that it would seek alternatives to increase access to the caucus. Blocking the states’ measures five months ahead of the first caucus leaves Iowa and Nevada little time to deliver an alternative.

“We are obviously disappointed by this outcome,” said Iowa Democratic Party Chair Troy Price, “but if the DNC does not believe the virtual caucus can be secure, then we cannot go forward.” He said he is confident in vendors providing virtual caucus technology. Nevada’s Democratic party did not respond to a request for comment.

Democrats focused on election security after the 2016 presidential race, when Russian intelligence officers hacked computers linked to the DNC and Hillary Clinton’s campaign, stole data, and staged releases of documents from the trove.

Law enforcement agencies have warned that U.S. election systems are vulnerable to interference ahead of the 2020 vote.