FBI agents have converged on the Oregon wildlife refuge where the last four followers of Ammon and Ryan Bundy remain holed up, the agency confirmed Wednesday night.
The FBI's Portland office said agents have been stationed at barricades in front of and behind the area of Malheur National Wildlife Refuge where the remaining occupiers are camping.
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Negotiations were under way, and no shots have been fired, the bureau said.
The remaining occupiers are believed to be: David Fry, 27, of Blanchester, Ohio; Jeff Banta, 46, of Elko, Nevada; and Sean Anderson, 48, and Sandy Anderson, 47, a married couple from Riggins, Idaho.
They're among 16 people — including the group's leaders, Ammon and Ryan Bundy — who were charged last week with conspiracy to impede federal officers in a grand jury indictment.
The confrontation began about 4:30 p.m. (7:30 p.m. ET) when one of the occupiers drove an all-terrain vehicle outside the group's own barricades, the FBI said. When agents approached the driver, he speeded back to the encampment, it said.
"We reached a point where it became necessary to take action in a way that best ensured the safety of those on the refuge, the law enforcement officers who are on scene and the people of Harney County who live and work in this area," said Greg Bretzing, special agent in charge of the FBI in Oregon.
"It has never been the FBI's desire to engage these armed occupiers in any way other than through dialogue," he said.
The occupation of Malheur, in central Oregon near Burns, began Jan. 2. The Bundys were arrested Jan. 26 during what authorities have described as a "traffic stop." The protest's main spokesman, Robert LaVoy Finicum, 54, was killed during a confrontation with police and the FBI during the stop.
The group's stated goals were the release of two ranchers who were ordered back to prison for burning public land and that the federal government turn over public land to local control.
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This story originally appeared on NBCNews.com.