PORTLAND, Ore. (Reuters) – Four anti-government activists still occupying a U.S. wildlife refuge in Oregon have been indicted along with 12 others previously arrested on charges of impeding federal officers during a month-long armed standoff at the compound.

The indictment, filed in federal court in Oregon and unsealed on Thursday, supersedes an earlier criminal complaint that charged protest leader Ammon Bundy and others with preventing officers and employees of the U.S. Fish and Wildlife Service from discharging their duties by “force, intimidation, and threats.”

Attorneys for the defendants were not immediately available for comment.

The occupation began Jan. 2, when Bundy, his brother Ryan and other followers took over the headquarters of the Malheur National Wildlife Refuge in remote eastern Oregon to protest federal control of millions of acres of public land in the West.

The three-page indictment says the defendants blocked federal agents in the performance of their duties, brandished firearms and refused to leave the refuge and threatened violence against anybody who attempted to remove them.

It also says the protesters recruited others in person and over social media to join their ranks, and warned the sheriff of Harney County in the nearby town of Burns of “extreme civil unrest” if their demands were unmet, among other acts of intimidation.

The Bundy brothers and nine others were arrested last week in Oregon, most of them during a confrontation with FBI and state police on a snow-covered roadside where a spokesman for the group, Robert “LaVoy” Finicum, was shot to death. A 12th member of the group turned himself in to authorities in Arizona.

Two of those arrested have since been released on condition that they wear electronic tracking devices while awaiting trial, leaving 10 of the former protesters, including the Bundys, still in custody.

Their immediate fate has been clouded by the four holdouts among the group, who joined the protest after it started but have so far refused to end their occupation of the refuge.

A judge has cited the continuing standoff as a major obstacle to the release of at least some of those who remain in custody. An attorney for arrested protester Jason Patrick, named in the indictment, referred to the holdouts as “four idiots” at odds with his client’s aims.

The indictment contains the same charges as those in the criminal complaint filed last month but avoids the need for prosecutors to seek a judge’s determination that sufficient evidence exists to proceed to trial.

(Reporting by Shelby Sebens in Portland, Oregon; Writing and additional reporting by Eric M. Johnson in Seattle; Editing by Steve Gorman and Dan Grebler)