The 2024 US presidential campaign has been a particularly volatile one, and security was ramped up given concerns over possible civil unrest, election chicanery and violence against poll workers.
Arizona, Georgia and Pennsylvania all reported hoax threats that in some cases briefly interrupted voting while police checked for bombs, though authorities did not report finding any explosives.
"The FBI is aware of bomb threats to polling locations in several states, many of which appear to originate from Russian email domains," spokeswoman Savannah Syms said in a statement.
"None of the threats have been determined to be credible thus far," she added, urging the public to "remain vigilant."
Georgia's Secretary of State Brad Raffensperger reported 60 threats in counties around the state, and identified Russian involvement without elaborating.
At least 10 voting sites in areas around Georgia's biggest city Atlanta were evacuated and searched, police in Fulton and DeKalb counties said.
"We are the descendants of, the sons and daughters of people who faced lynch mobs, water cannon... to exercise the right to vote. And so we aren't going to let bomb threats turn us around," Kobi, the mayor of South Fulton who goes by one name, told AFP.
Pennsylvania Governor Josh Shapiro told reporters that multiple bomb threats were called in to polling sites and public buildings across the state, but none appeared to be credible.
Arizona, which reported four threats, pointed toward apparent Russian involvement.
"We have reason to believe, though I won't get into specifics, that this comes from one of our foreign enemies -- namely Russia," Arizona's Secretary of State Adrian Fontes said.
"They've been busy lately."
'Smelled like fuel'
With Democrat Kamala Harris and Republican Donald Trump deadlocked at the climax of the 2024 race, authorities were keen to reassure jittery Americans that their votes were secure.
They have bolstered physical security for election operations nationwide.
Poll workers have been given panic buttons, special weapons teams have been deployed on rooftops and hundreds of National Guard personnel have been placed on standby.
The FBI set up a national election command post in Washington to monitor threats 24 hours a day through election week.
The US Capitol Police, who protect the seat of Congress in Washington, arrested a man Tuesday who "smelled like fuel" and was carrying a lighter and accelerant.
He was stopped at the Capitol visitor center -- part of the complex that was stormed by Trump supporters in a deadly riot on January 6, 2021, as they sought to overturn his election loss to Joe Biden.
Police Chief J. Thomas Manger later told a news conference that the man had "papers" he intended to deliver to Congress and that it was unclear if he was planning to light himself on fire.
"There's no indication, right now, that it had anything to do with the election," he said.
