(POLITICO) — The USDA says it closed six offices in five states today after receiving a series of anonymous threats.

The department closed offices in Fort Collins, Colo.; Hamden, Conn.; Beltsville, Md.; Raleigh, N.C.; and Kearneysville and Leetown, W.Va. A USDA spokesman said the FBI is investigating the threats, sent in an email to multiple employees at each of the locations. The department declined to give more information on what the messages contained, but Agriculture Secretary Tom Vilsack, in a memo to USDA employees, described them as “serious [in] nature.”

“USDA is working closely with federal and local law enforcement, including the Federal Bureau of Investigation, to determine whether the threats are credible,” the spokesman, Matthew Herrick, said in a statement. “Personnel at these locations have been made aware of the threats and will not report to these offices until further notice.”

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