Election officials in Florida have rejected a suggestion that the state's preparations for the presidential election are seriously flawed.
Carter is respected outside America as an electoral observer
Jimmy Carter, the former US president and veteran election monitor, predicted polling in the key state would be neither free nor fair.
A spokesman for Florida's election body told the BBC it was disappointed by the former president's remarks.
He said Mr Carter seemed "misinformed" about the true state of preparations.
"I think there's some misinformation in it and we're disappointed that he didn't contact us to ensure accurate, up-to-date information," the spokesman said.
The BBC's Jill McGivering notes that some may point to Mr Carter's political loyalty to the Democrats as a way of dismissing his comments.
Others may argue his longstanding work with the Carter Centre, monitoring elections worldwide, makes him a credible authority, our correspondent says.
The row could also revive the bitterness felt by many Democrats last time when George W Bush won the state and the presidency after a long, legal battle about the Florida vote, she adds.
Mr Carter made his comments in an opinion piece published in the Washington Post on Monday.
"The disturbing fact is that a repetition of the problems of 2000 now seems likely," he wrote.
Touch-screen machines were introduced in the state after that election when punch-cards were responsible for delaying the outcome of the race, which Mr Bush won in Florida against Al Gore by a mere 537 votes.
Mr Carter said that Florida's top election official in 2004, Glenda Hood, showed "strong bias".
He accused of her of favouring Republicans by trying to get the name of independent presidential candidate Ralph Nader included on the state ballot, knowing he might divert Democrat votes.
The former president also alleged that an attempt had been made to disqualify black Americans more likely to vote Democrat on the basis of criminal records.
Alia Faraj, a spokeswoman for Ms Hood, said she was "disappointed that a statesman like former President Carter would submit such a letter".
Florida led the US in "election reform", the spokeswoman said, adding that the state run by Governor Jeb Bush, the current president's brother, had held hundreds of successful elections since new systems were put in place in 2002.
The spat over Florida comes just days before the first TV debate between Mr Bush and John Kerry, who will meet in Miami, Florida.
They are expected to discuss the war on Iraq and homeland security during the programme on Thursday.
Both men have cut back on their campaign touring to go behind closed doors and rehearse the arguments and techniques they will need during a series of three debates to be held over two weeks.
Each has held mock debates with aides standing in for their opponent.
Tens of millions of television viewers are expected to watch Thursday's head-to-head.
Mr Kerry, a debating champion at high school and college, will hope it can help him claw back a deficit in the polls variously put between 3% and 9%.