WASHINGTON -- The FBI is warning police across the country that an anti-government group's call to remove governors from office could provoke violence.

The group called the Guardians of the free Republics wants to "restore America" by peacefully dismantling parts of the government, according to its Web site. It sent letters to governors, including South Carolina's Mark Sanford, demanding they leave office or be removed.

Investigators do not see threats of violence in the group's message, but fear the broad call for removal of top state officials could lead others to act out violently. At least two states beefed up security in response.

S.C. Law Enforcement Division Chief Reggie Lloyd said Friday that the letter was mailed to Sanford on Monday. Lloyd said the letter was turned over to the governor's protective detail.

As of Wednesday, more than 30 governors had received letters saying if they don't leave office within three days they will be removed, according to an internal intelligence note by the FBI and the Department of Homeland Security. The note was obtained by The Associated Press.

The FBI warning comes at a time of heightened attention to far-right extremist groups after the arrest last weekend of nine Christian militia members accused of plotting violence.

In explaining the letters sent to the governors, the intelligence note says officials have no specific knowledge of plans to use violence, but they caution police to be aware in case other individuals interpret the letters "as a justification for violence or other criminal actions."

The FBI associated the letter with "sovereign citizens," most of whom believe they are free from all duties of a U.S. citizen, such as paying taxes or needing a government license to drive.

A small number of these people are armed and resort to violence, according to the report.