A group of anonymous e-mail messages prompted the closure of U.S. Department of Agriculture offices across the nation on Tuesday, including a U.S. Forest Service facility in Fort Collins.

The USDA said the messages were received by the agency on Monday and concerned officials about the safety of department personnel. Officials did not elaborate.

The closed offices spanned five states and six different locations, including Hamden, Conn.; Beltsville, Md.; Raleigh, N.C.; and Kearneysville and Leetown in W.V.

The shuttered Fort Collins office holds the U.S. Forest Service’s building at 2150 Centre Ave., which houses the Canyon Lakes Ranger District headquarters for the Arapaho and Roosevelt national forests. The Forest Service is under the auspices of the USDA.

The USFS office in Fort Collins tweeted that it was closed Tuesday because of unspecified safety concerns. A spokesman for the Forest Service’s Rocky Mountain region directed questions on the situation to a national office.

Our office is closed today for safety concerns, including our Info Center. Check our website for recreation info: https://t.co/GqpUfOICgB — Canyon Lakes RD (@usfsclrd) August 30, 2016

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

USDA agencies impacted by the closures include the Animal and Plant Health Inspection Service, Agricultural Research Service, Food Safety Inspection Service, Forest Service, National Agricultural Library, Natural Resources Conservation Service, Office of the Inspector General and USDA Departmental Management.

In total, about 1,500 employees are affected by the closures, the USDA says, including roughly 200 in Fort Collins.

The USDA said it would share updates on the situation as more information becomes available.

Parking lot outside of Building B here in Fort Collins. Empty because of anonymous threat to USDA. #Denver7 pic.twitter.com/yBy4yhj9aW — Amanda del Castillo (@AmandaDTV) August 30, 2016

The Larimer County Sheriff’s Office said it was not called to the Fort Collins office as part of the closure and Fort Collins police did not immediately return a voicemail seeking comment.

Other Forest Service and USDA offices in Colorado do not appear to be affected.