The Federal Bureau of Investigation is looking into suspicious, possibly threatening letters mailed last week to Utah Gov. Gary Herbert and several other governors.

The letter contained no specific threat of violence, but it has nonetheless triggered an FBI probe -- and increased security coverage for Herbert and the area of the Utah Capitol, state and federal officials, said a Salt Lake Tribune tribune report.

 

However, the letters reportedly demand that the governors resign within three days and re-take an oath of office, or be removed. The letters have been variously linked to the right-wing, anti-government groups Sovereign Citizen and The Guardians of the Free Republics.

 

The report said that while the letters contain no specific threats, the FBI is looking into the groups to determine whether "they advocate any violence" as part of a call to overthrow the government or remove its officials.