The FBI has seized ballots cast in the primary and general elections in one county after allegations of improprieties were raised.

"There is an ongoing investigation into election fraud, but I can't go into any details due to the nature of the investigation," FBI spokesman Daron Borst said Friday from Las Vegas.

Eureka County clerk-treasurer Mary Jo Castaneda said ballots from both elections were seized Nov. 18 after a complaint was made about the residency of about 85 voters.

A source familiar with the allegations who asked not to be identified said questions were raised about whether some of the voters lived in the county and whether others were even alive.

Castaneda said it was her understanding some of the voters had moved to another home in Eureka County, but Borst said the challenges went beyond simple postelection gripes.

"To open one of these investigations requires Department of Justice approval, so it's not based on a mere allegation of wrongdoing by a disgruntled candidate or citizen," he said.

"It had to be something meritorious on its face for us to proceed."

More than 680 Eureka County voters cast ballots in the general election in November and about 580 voted in September's primary.

The Eureka County probe marked the second time this year the FBI has become involved in a county election in Nevada.

Two agents confiscated Nye County voter registration records and absentee ballots in Tonopah from the Nov. 5 election. The seizure came a month after a District Court judge in Pahrump scratched almost 5 percent of the county's 18,667 registered voters from the voter rolls, saying they either were dead or didn't live where they said they did.

Borst would only confirm that an investigation was under way in Nye County as well as in Eureka.

He said the agency became involved because the challenged elections involved either a federal race or issue.

The Nevada secretary of state's office said it was aware of the challenges, but had not been consulted by the FBI since it was a federal matter.

Castaneda said the number of challenged votes would not be enough to affect the results of any races in Eureka County, including that of her successor, Frances Gale.