In the message, which was obtained by NBC, a voice that sounds like the president tells the listener “Your vote makes a difference in November, not this Tuesday” – referring to the New Hampshire primary.
“It’s important that you save your vote for the November election,” the message says. “Voting this Tuesday only enables the Republicans in their quest to elect Donald Trump again.”
The AG’s office said the messages “appear to be an unlawful attempt to disrupt the New Hampshire Presidential Primary Election and to suppress New Hampshire voters”.
“Although the voice in the robocall sounds like the voice of President Biden, this message appears to be artificially generated based on initial indications,” a statement from the department read.
“The message appears to have been ‘spoofed’ to falsely show that it had been sent by the treasurer of a political committee that has been supporting the New Hampshire Democratic Presidential Primary write-in efforts for President Biden.
“The message’s content directed recipients who wished to be removed from a calling list to call the number belonging to this person.”
The statement continued: “These messages appear to be an unlawful attempt to disrupt the New Hampshire Presidential Primary Election and to suppress New Hampshire voters.
“New Hampshire voters should disregard the content of this message entirely.”
The office added that an investigation by its Election Law Unit is ongoing.
The message concludes with a phone number belonging to Kathy Sullivan, a former New Hampshire Democratic Party chair, according to NBC.
Ms Sullivan told the outlet that while it was not clear who was behind the robocall, “It’s obviously somebody who wants to hurt Joe Biden.”
“I want them to be prosecuted to the fullest extent possible because this is an attack on democracy,” she said. “I’m not going to let it go. I want to know who’s paying for it? Who knew about it? Who benefits?”
Ms Sullivan said she also plans to engage federal law enforcement.
Biden campaign manager Julie Chavez Rodriguez told NBC "the campaign is actively discussing additional actions to take immediately."
The incident comes amid concerns over the effects of AI on election security ahead of the general election in November.
According to the Brennan Center for Justice, AI “poses a major and immediate threat to election offices and election system vendors”.
“It excels at imitating authoritative sources, making it easier to deceive specific individuals or the general public by impersonating election officials or forging official election documents,” an article on the centre’s website states.