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A group of protesters and purported militiamen remained in a federal building at an Oregon wildlife refuge Sunday night, a day after they occupied it and vowed to stay indefinitely to highlight ranchers' rights.

The standoff came after so-called "militia members" converged on the small town of Burns to show support for a pair of ranchers jailed on an arson conviction, according to NBC station KTVZ of Bend.

After a march and rally there, a small group then took over the Malheur National Wildlife Refuge headquarters about 60 miles away.

Ammon Bundy — son of Cliven Bundy, the Nevada rancher known for his armed 2014 standoff with the federal government — was among them.

Bundy first issued a Dec. 31 video urging "patriots" to "stand up" and report to Burns by Jan. 2.

"There's been leaders of different militia groups, different organizations that have called for a stand-down, and I am wanting to talk to the individual, to the patriot, that this is not a time to stand down. It is a time to stand up and come to Harney County," Bundy said in the video. "No matter what your leader says ... you need to draw your own conclusions."

Bundy said in a video posted to Facebook late Saturday that his group was there and prepared "to be out here for as long as needs be."

"Once they can use these lands as free men, then we will have accomplished what we came to accomplish," he said.

Bundy later told KTVZ that "it's the people's facility — owned by the people."

"And it has been provided for us to be able to come together and unite in making a hard stand against this overreach — this taking of the people's land and resources," Bundy said.

The Harney County Sheriff's Office said Sunday that the group of protesters claimed to be part of "militia groups supporting local ranchers, when in reality these men had alternative motives to attempt to over throw the county and federal government in hopes to spark a movement across the United States."

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The sheriff's office asked residents to stay away from the refuge "for their safety."

"We are currently working jointly with several organizations to make sure the citizens of Harney County are safe and this issue is resolved as quickly and peaceful as possible," the sheriff's office statement said.

A U.S. Fish and Wildlife Service representative said the bureau had received reports that "an unknown number of individuals have broken into the Malheur National Wildlife Refuge facility" — but no staff were inside of the building at the time.

"While the situation is ongoing, the main concern is employee safety," the spokesman said.

The protests were making some Burns residents uneasy.

Bundy stressed that the protest was peaceful, saying his group poses "no threat to anybody."

At least one person could be seen in video with a gun, but it was unclear what kind of weapons the protesters had or whether they were part of any larger organization — although local residents were visibly worried and had even posted signs saying "Militia go home."

"It's sort of frightening when there are people making threats and people toting guns," Burns resident Kainan Jordan told KTVZ. "We're not used to this kind of thing here."

Sen. Ron Wyden, D-Oregon, said he understands the frustrations of some of Oregon's residents, "but the next step from frustration is not to walk off a cliff misled by some outsiders who seem willing to take the law into their own hands." He said he would work on developing "solutions rather than standoffs."

Largely, the protesters sang, toted signs and American flags and threw pennies at the Harris County Courthouse, which was symbolic of their effort to buy back their government, according to The Associated Press.

The FBI said it was aware of the situation but declined to comment further. NBC News was unable to reach local officials for further comment.

The case that sparked the initial protest involves Dwight Hammond, 73, and his son Steven, 46, who set fires that spread to government lands they leased to graze cattle.

The Hammonds — who said they lighted fires in 2001 and 2006 to reduce the growth of invasive plants and protect their property from wildfires — were convicted and served time for arson.

However, a judge later ruled that their sentences — three months for the father, one year for the son — were too short and ordered them back to prison.

Prosecutors argued that the earlier fire, which burned 139 acres of public land, was set "shortly after Steven Hammond and his hunting party illegally slaughtered several deer" on the property, according to a U.S. Justice Department statement. The fire "destroyed all evidence of the game violations," the statement said.

The Hammonds are due to report to jail on Monday, according to KTVZ.

Cliven Bundy urged the Hammonds to turn themselves in, but he said in a statement that "the United States Justice Department has NO jurisdiction or authority within the State of Oregon, County of Harney over this type of ranch management."

Bundy told Oregon Public Broadcasting on Saturday that "the people had to do something" but that he wasn't a part of the protests.

On Saturday, supporters also gathered outside the elder Hammond's home and hugged him and his wife one by one in a display of solidarity, KTVZ reported.

"It isn't my decision, obviously. It's a sentence," Hammond said, adding that he appreciated the support from the protesters.

"I thank everyone who came out here today," Hammond said. "See you in five years."