Hoax bomb threats, many of which appeared to originate from Russian email domains, were directed at polling locations in three battleground states - Georgia, Michigan and Wisconsin - as Election Day voting was underway, the FBI said on Tuesday.
"None of the threats have been determined to be credible thus far," the FBI said in a statement, adding that election integrity was among the bureau's highest priorities.
At least two polling sites targeted by the hoax bomb threats in Georgia were briefly evacuated on Tuesday.
Those two locations in Fulton County both re-opened after about 30 minutes, officials said, and the county is seeking a court order to extend the location's voting hours past the statewide 7pm deadline.
Republican Georgia Secretary of State Brad Raffensperger blamed Russian interference for the Election Day bomb hoaxes.
"They're up to mischief, it seems. They don't want us to have a smooth, fair and accurate election, and if they can get us to fight among ourselves, they can count that as a victory," Raffensperger told reporters.
The Russian embassy in Washington did not immediately respond to a request for comment.
It was not immediately clear how many hoax bomb threats were received in Michigan and Wisconsin.
Adrian Fontes, a Democrat and the Arizona Secretary of State, the chief election official in the swing state, said four fake bomb threats had been delivered to polling sites in Navajo County, Arizona.
"Vladimir Putin is being a prick," Mr Fontes said, referring to the Russian president.
Ann Jacobs, head of the Wisconsin Elections Commission, said fake bomb threats were sent to two polling locations in the state capital of Madison, but did not disrupt voting. Jacobs did not know if the threats were linked to Russia.
An FBI official said that Georgia alone received more than two dozen, most of which occurred in Fulton County, which encompasses much of Atlanta, a Democratic stronghold.
A senior official in Raffensperger's office, speaking on the condition of anonymity to speak freely, said the Georgia bomb hoaxes were sent from email addresses that had been used by Russians trying to interfere in previous U.S. elections.
The threats were sent to U.S. media and the two polling locations, the official said. "It's a likelihood it's Russia," the official said.
Democratic Vice President Kamala Harris and Republican former President Donald Trump are locked in a tight race to win the White House. Opinion polls suggest the contest is too close to call.
The phony bomb threats mark the latest in a string of examples of alleged interference by the Russians in the 2024 election.
On November 1, US intelligence officials warned that Russian actors manufactured a video that falsely depicted Haitians illegally casting ballots in Georgia. Intelligence officials also found that the Russians created a separate phony video which falsely accused someone associated with the Harris presidential ticket of taking a bribe from an entertainer.
US intelligence officials have also accused Russia of interfering in previous U.S. presidential elections, especially the 2016 race which Trump won against Democratic candidate Hillary Clinton
