Ammon Bundy and 15 others accused in the armed takeover of a federal wildlife refuge -- including four people who remain at the bird sanctuary -- have been indicted on a charge of conspiracy to impede federal officers through intimidation, threats or force.

A federal grand jury returned the indictments Wednesday and they were unsealed Thursday morning.

They accuse Ammon Bundy, the leader of the monthlong armed occupation of the Malheur National Wildlife Refuge outside Burns, and the other key players of conspiring to prevent employees of the U.S. Fish & Wildlife Service from working at the refuge, taking over the property armed with firearms and intimidating the people of Harney County.

The alleged offenses began Oct. 5, when two of the defendants met with the Harney County sheriff to warn of "extreme civil unrest'' if their demands were unmet, according to the indictments.

All are accused of occupying the federal property "while using and carrying firearms,'' threatening violence against anybody who attempted to remove them from the refuge and using social media and other means of communication to recruit and encourage others to join them.

The indictments also allege the group carried firearms on the federal property and refused repeated federal orders to leave. They contend the conspiracy lasted through the date of the indictments.

Ammon Bundy, brother Ryan Bundy and other key players who were arrested last week are named in the indictments, as well as the four holdouts who remain on the federal property and a man who was the first to be arrested in early January, then accused of driving a government truck off the refuge.

The likely reason the federal government stayed with the single conspiracy charge is because that's what prosecutors believe they can prove at this time without having a chance yet to examine any potential damage to the refuge and artifacts stored there since the occupation began.

The defendants will be arraigned on the indictments Feb. 24.

The conspiracy charge is a felony and carries a maximum six-year prison sentence and fines. The case has been assigned to U.S. District Court Judge Anna J. Brown.

Bundy, the son of controversial Nevada rancher Cliven Bundy, led a group of followers to the refuge Jan. 2 and took over the headquarters, demanding the release of two local ranchers from prison and local control of federal land in Harney County.

Named along with the Bundys are Jon Ritzheimer, Joseph O'Shaughnessy, Ryan Payne, Brian Cavalier, Shawna Cox, Peter Santilli, Jason Patrick, Duane Leo Ehmer and Dylan Anderson.

Also indicted are four still at the refuge: Sean Anderson, David Lee Fry, Jeff Wayne Banta and Sandra Lynn Pfeifer Anderson.

Finally, Kenneth Medenbach, arrested in January in Burns and accused of driving a government truck off the refuge property, is also named.

For the first three weeks, federal agents and state police mostly stayed out of sight, taking a "wait-them-out'' approach. On Jan. 26, that changed as federal agents and state police stopped the Bundys and other leaders as they were driving in two vehicles to a meeting in John Day.

The police stops were made along rural, tree-lined U.S. 395. The Bundy brothers, and other leaders, including Ryan Payne, body guard Brian Cavalier and follower Shawna Cox were arrested.

Occupation spokesman Robert "LaVoy" Finicum, 54, was shot and killed by state police after he sped away from the stop, rammed into a snowbank and then emerged from his truck with his hands up but then reached twice into the inner pocket of his jacket, according to the FBI. He had a loaded 9 mm pistol on him, the FBI said.

Two others associated with the occupation were arrested in Burns, three were arrested at an FBI checkpoint when leaving the refuge and another surrendered to authorities in Arizona.

These are the defendants named in the indictments: Ammon Bundy, 40, of Emmett, Idaho; Jon Ritzheimer, 32, of Peoria, Arizona; Joseph O'Shaughnessy, 43, of Cottonwood, Arizona; Ryan Payne, 32, of Anaconda, Montana; Ryan Bundy, of Bunkerville, Nevada; Brian Cavalier,44, of Bunkerville, Nevada; Shawna Cox, 59, of Kanab, Utah; Peter Santilli 50, of Cincinnati; Jason Patrick, 43, of Bonaire, Georgia; Duane Leo Ehmer, 45, of Irrigon; Dylan Anderson; Sean Anderson, 47; David Lee Fry, 27, of Blanchester, Ohio; Jeff Wayne Banta, 46, of Elko, Nevada; Sandra Lynn Pfeifer Anderson, 48; and Kenneth Medenbach, 62, of Crescent. The Andersons recently moved from Wisconsin to Idaho.

Detention hearings are scheduled at 1:30 p.m. Thursday afternoon in U.S. District Court in Portland for Cavalier and Ehmer. Santilli will be back in court at 4 p.m. for his continued detention hearing.

-- Maxine Bernstein

mbernstein@oregonian.com

503-221-8212

@maxoregonian