The twin reports highlighted risks to the elections and strategies for mitigating them, at a time when one man has been charged over armed attacks on a Democratic party office, and police in Oregon and Washington are investigating suspected arson attacks on ballot boxes in which some ballots were destroyed.

The GPAHE report’s warning is based on a rise in violent chatter on platforms known for hosting extremist content, including Telegram, Gab, Communities.win, and some communities across the decentralized social media network known as the Fediverse.

The report shows that while the overall volume of messages on these platforms may be lower than in 2020, the sharp rise in violent rhetoric follows a pattern set ahead of the 2020 election.

For example, in October, violent rhetoric related to election denialism increased by 317% on Telegram, 105% on Gab, 25% on communities.win, and 75% across a selection of Fediverse communities.

The report says that across these platforms, users are indulging in violent rhetoric linked to election denialism. Some posts on Telegram this year have used election denialism to justify calls for violence, including calls for an “inevitable civil war” and urging users to “shoot to kill any illegal voters”.

• Don’t miss important US election coverage. Get our free app and sign up for election alerts

On Gab, users have threatened perceived election fraudsters with treason charges, calling for “firing squads” or “the rope”, according to the report. It notes calls on the platform for “public executions for all voter fraud” and the shooting of elected officials labeled as “traitors”, along with copious antisemitic conspiracy theories.

Communities.win is a collection of forums that includes The_Donald, which was banned from Reddit for hate speech in 2020. According to the GPAHE report, users there have fantasized about a civil war in recent weeks, claiming that Democrats will not relinquish power and that a violent uprising is necessary for a “Great Awakening”, a concept previously popularised by the QAnon conspiracy movement.

In Fediverse communities, users have shared posts blaming the “liberal media” for inciting a “war” and encouraging violence against perceived political opponents.

GPAHE’s report warns that “ignoring these worrying trends will only risk further acts of violence related to election denialism and anti-democratic sentiment”.

Hiedi Beirich, GPAHE’s co-founder, told the Guardian: “Our report shows that, when compared to violent election denial chatter in 2020, the numbers have been lower so far this year, but they are quickly rising as we approach Election Day.”

She added that “unmoderated fringe sites” were seeing “rising numbers of comments with violent political rhetoric “ and “posts targeting election workers with violence, a sign that real world activity could escalate”.

BDI, meanwhile, warns against complacency after 2022, when vigilante poll watchers mostly stayed away from drop boxes, despite months of conspiracy-minded chatter about Democrats and the “Deep State” stealing mid-term elections from Republicans.

According to the fact sheet, BDI data shows that in 2022, there were 44 incidents of physical monitoring at fewer than 20 drop box locations out of an estimated 13,000 active sites nationwide. That is, only 0.1% of drop boxes around the country were subject to monitoring activity.

It warns, however, that threats of monitoring activity have resurfaced online during the 2024 campaign, and states including Arizona and Wisconsin have seen legal decisions that reduce restrictions on vigilante monitoring, opening the way for possible voter intimidation.

The Guardian reported this week on an Arizona poll-watching group which has been casting doubt on the election result ahead of time, with members’ paranoia being fueled by rightwing influencers and media outlets.

The fact sheet makes a series of recommendations to poll workers ahead of the vote on ways to head off political violence, including de-escalation techniques; research to identify threats; communicating accurate information on elections; and community outreach and dialogue on election security.

The BDI report says that “these steps can improve the U.S. political violence early warning infrastructure and help prevent the amplification of rumors, false claims, and unfounded threat messaging aimed at suppressing voter turnout in targeted communities”.