BILLINGS, Mont. (AP) — Federal employees overseeing U.S. public lands were assaulted or threatened at least 360 times over a five-year period marked by heightened tensions with anti-government groups and dwindling ranks of law enforcement officers, a congressional watchdog agency said Monday.

The Government Accountability Office in a new report highlights anti-government tensions that at times have boiled over, including a six-week armed occupation of a federal wildlife refuge in Oregon in 2016 and other standoffs with armed protesters in Montana and Nevada.

The clashes have been rooted in a deep distrust of government on the part of the protesters, who view the federal bureaucracy as unlawfully impeding people from using public land for grazing, mining and other economic purposes.

Even a routine traffic stop or the collection of a park entrance fee can be enough to trigger an assault or threat, according to GAO investigators.

The incidents investigators cataloged during interviews with federal workers ranged from threatening phone calls and gunshots fired over the heads of employees, to the stabbing of a Bureau of Land Management worker outside a federal building.

Some of the assaults triggered FBI domestic terrorism investigations, although the precise number was not disclosed because it was considered sensitive information.

The report did not say whether rates of assaults and threats were increasing. But it noted a dwindling number of federal officers patrolling the nation’s vast forests, parks, wildlife refuges and other open spaces, which cover more than 670 million acres primarily in 12 Western states.