In a statement, authorities said they placed agents at barricades both immediately ahead of and behind the area where the occupiers were camping. An acquaintance of occupier David Fry was livestreaming on YouTube what he said was an open phone line from the standoff. The occupiers said they were surrounded by armored vehicles. They can be heard arguing with someone they said was a negotiator.
The four holdouts were the last remnants of an armed group that seized the Malheur National Wildlife Refuge in eastern Oregon on Jan. 2 to oppose federal land-use policies.
The FBI said that one of the occupiers rode an ATV on Wednesday afternoon outside the barricades "established by the militia" at the refuge. When agents tried to approach the driver, the FBI said he returned to their camp at a high rate of speed.
The four had refused to leave even after group leader Ammon Bundy and others were arrested on a remote road outside the refuge on Jan. 26. The traffic stop also led police to shoot and kill Arizona rancher Robert "LaVoy" Finicum, who the FBI says was reaching for a gun.
Authorities then surrounded the refuge and later got the holdouts added to an indictment charging 16 people with conspiracy to interfere with federal workers. The four previously said they would not leave without assurances they would not be arrested.
They were: Fry, 27, of Blanchester, Ohio; Jeff Banta, 46, of Elko, Nevada; and married couple Sean Anderson, 48, and Sandy Anderson, 47, of Riggins, Idaho.
They recently posted a series of defiant videos in which Fry shows a defensive perimeter they have built and takes a joyride in a government vehicle. Fry says the FBI told him he faces additional charges because of the barricades.
He said the four have "every right" to defend themselves against a government raid. Fry then drives around in a federally owned truck, saying, "Now you've got another charge on me FBI. I'm driving your vehicle."
His father, William Fry, has said he was disappointed that his son was charged, saying he is no different than those who believe "our country is heading in the wrong direction."
Banta's father, Willard Banta, has said he worried about how the takeover would end. But he sympathized with the occupiers' frustrations with federal land managers, saying, "I support them 100 percent."
At first, Bundy urged the last holdouts to go home. But in response to the grand jury indictment, he took a more defiant tone from jail.
Bundy called his jailed followers "political prisoners" who were trying to educate ranchers and others about their constitutional rights on federal lands and abuses by U.S. authorities.