(Reuters)

A public Facebook group pushing false claims about voter fraud and Democrats trying to “steal” the U.S. election rapidly swelled to more than 325,000 members today (November 5), a day after it was created.

The “Stop the Steal” group, which says it was started by the conservative non-profit Women for America First, called for “boots on the ground to protect the integrity of the vote”.

With tensions rising, about 200 of Republican President Donald Trump’s supporters, some armed with rifles and handguns, gathered outside an election office in Phoenix, Arizona, on Wednesday following unsubstantiated rumors that votes were not being counted.

In Detroit, officials blocked about 30 people, mostly Republicans, from entering a vote-counting facility amid unfounded claims that the vote count in Michigan was fraudulent.

It is normal in U.S. elections for states to count votes for days, or sometimes even weeks, after voting ends. Election experts say fraud is very rare in U.S. voting.

Unfounded and debunked claims about the integrity of Tuesday’s election have spread on social media by Trump and high-profile Republican accounts and the hashtag #StopTheSteal has gained momentum.

Facebook groups are billed as community forums for shared interests but watchdog organisations and social media researchers have argued that they can be hotbeds for hyper-partisan misinformation.

The Stop the Steal group’s description says: “Democrats are scheming to disenfranchise and nullify Republican votes. It’s up to us, the American People, to fight and to put a stop to it.”

The group directed new members to an email sign-up page “in the event that social media censors this group”.

The group’s administrations and moderators included veteran Tea Party activist Amy Kremer and her daughter Kylie, as well as Jennifer Lawrence and Dustin Stockton, two members of the group We Build the Wall, which were raided by federal agents in August as part of a fraud investigation.

Attempts to reach administrators and moderators on Facebook were not immediately successful. An email and a telephone message left with Women for America First was not immediately returned.

Several Facebook events billed as “Stop the Steal” protests and caravans also laid out plans for users to gather in states across the country.