A staff member of the U.S. House Permanent Select Committee on Intelligence, which oversees the nation's intelligence operations, said he had heard of no such plot.

And Indiana officials in the county where the power grid is located were at a loss to explain where the information originated.

In an interview Tuesday, Harris would not reveal the name of the mayor who told her about the threat or provide further details.

She said in the speech that a man of Middle Eastern heritage had been arrested in the plot and that explosives were found in his home in Carmel, a suburb north of Indianapolis.

Carmel Mayor James Brainard and a spokesman for Indiana Gov. Joe Kernan said they had no knowledge of such a plot. Brainard said he had never spoken to Harris.

Harris, a Republican who is running for re-election, said the case was an example of the nation's success in fighting terrorism.

Floyd Jay Winters, one of four Democrats running for the nomination to oppose Harris in this fall's election, called it irresponsible to bring up allegations at a rally but provide no details.

Harris first gained worldwide attention during the 2000 presidential election when she served as Florida's secretary of state and was often harpooned by cartoonists and late night television talk show hosts from everything from her clothes to the makeup she wore.

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Editor's note: