US regulators on Thursday declared scam "robocalls" made using voices created with artificial intelligence (AI) as illegal.

The phenomenon gained attention last month when a robocall impersonation of US President Joe Biden urged people to not cast ballots in the New Hampshire primary.

"Bad actors are using AI-generated voices in unsolicited robocalls to extort vulnerable family members, imitate celebrities, and misinform voters," Federal Communications Commission (FCC) chairwoman Jessica Rosenworcel said in a release.

"State Attorneys General will now have new tools to crack down on these scams."

The FCC unanimously ruled that AI-generated voices are "artificial" and thus violate a Telephone Consumer Protection Act (TCPA).

The TCPA is the primary law the FCC uses to curb junk calls, restricting telemarketing calls and the use of automated dialing systems.

The ruling makes voice cloning used in robocall scams illegal, allowing those behind such operations to be prosecuted, according to the FCC.

Previously, law enforcement agencies could prosecute people for the outcomes of scams such as fraud committed with the help of robocalls, but not the calls themselves, regulators said.

The prevalence of such calls has rocketed in recent years with the help of automated calling systems, some of which even "spook" phone numbers to make them appear to be from someone local.

A coalition of 26 state attorneys general were among those who urged the FCC to restrict use of AI-generated voices in telemarketing calls.

"Technology is advancing and expanding, seemingly, by the minute, and we must ensure these new developments are not used to prey upon, deceive, or manipulate consumers," Pennsylvania Attorney General Michelle Henry said in a letter from the coalition to the FCC in January.

"This new technology cannot be used as a loophole to barrage consumers with illegal calls."

The Attorney General for New Hampshire on Tuesday said the deepfake robocall of Biden was traced to a Texas company that shares ownership with companies that provide robocalls to politicians.

The official estimated that between 5,000 and 25,000 calls were made using Biden's impersonated voice.

Experts fear a deluge of deepfake disinformation in the 2024 White House race as well as in key elections around the globe this year.