Madison FBI supervisor Shawn Johnson says it's highly unlikely the threat is real.
He says there's nothing in the letters pointing toward motive or legitimacy and they don't appear to be the work of an organized terrorist outfit.
But the bureau and the state Department of Criminal Investigation are still investigating. Johnson says the letters are being analyzed at the state crime lab right now for fingerprints and other clues.
The FBI says the state agriculture secretary and Madison media outlets got a letter yesterday in which a group claims to have planted land mines in farm fields around Fort McCoy and in every county in Wisconsin.
A copy obtained by The Capital Times indicates the sender is from a "small, dedicated group'' that has planted anti-tank mines in every town surrounding Fort McCoy near Sparta, and five mines in every other county.
The letter is addressed to Governor Doyle. It says the reason for the group's action is to prove it can be done. And that the group would disclose the locations of the mines three weeks after mine clearing efforts begin.