U.S. authorities worked Monday to end a standoff at a federal wildlife center in the northwestern state of Oregon, where armed anti-government protesters took over the facility and declared they are prepared to stay for years.

White House spokesman Josh Earnest said President Barack Obama is aware of the situation and "hopeful it can be resolved peacefully and without violence."

The Federal Bureau of Investigation said it is working with local and state law enforcement officials to try to resolve the situation.

Demonstrators said they took over the remote facility at the Malheur National Wildlife Refuge in solidarity with two ranchers, Dwight Hammond, 76, and his son, Steven, 46, who are facing extended prison sentences for setting fires on federal land in the area they had used to graze their cattle.

Malheur National Wildlife Refuge, Oregon, US

They originally were given shorter sentences, but a federal appeals court ruled in October that the first judge erred in ignoring the mandatory minimum sentence for the crime, and it said they should be given five-year terms.

The two men turned themselves in Monday to resume their prison terms. Their attorneys said they would seek clemency from President Barack Obama to win their freedom again.

The armed protesters, making up a loosely organized group, said they have as many as 100 people with them.  They are being led by Ammon Bundy, whose family was at the center of a 2014 standoff over grazing rights on federal lands.

"We will be here as long as it takes," Bundy told reporters Sunday.  "We have no intentions of using force upon anyone. If force is used against us, we would defend ourselves."

Ryan Bundy talks on the phone at the Malheur Natio
Ryan Bundy talks on the phone at the Malheur National Wildlife Refuge near Burns, Ore., Sunday, Jan. 3, 2016.

Bundy said their case is a symptom of a "huge, egregious problem," happening across the country with the government imposing too many restrictions on land use and causing economic harm to local populations.

A sign in front of the occupied refuge building accuses the government of "doing what they do best, ABUSING POWER."

'Light up the whole country'

The Hammonds said they started the fires on their property to kill invasive species and then the flames spread to the federal land by accident.  But witnesses said they illegally killed deer, then distributed matches to others to be lit and dropped to "light up the whole country on fire."

A Hammond family statement says the two men only want to turn themselves in and serve out their prison terms. The family says no "patriot group or individual has the right or authority to force an armed standoff...against their wishes."

The anti-government militiamen who took over the wildlife refuge are angry that the court ruled to send the Hammonds back to prison, with credit for the time they already have served.

After the peaceful protest in the nearby town of Burns, the group took over the offices at the refuge, which were closed at the time.  Photographs showed the militia members moving fuel and food onto the refuge.

WATCH: Video footage from the scene

Federal ownership of western lands

Bundy and his father Cliven held a month-long armed standoff with federal authorities in 2014 over unpaid fees the government said they owed for letting their cattle graze on federal land in Nevada.  Hundreds of supporters joined the Bundys and eventually the government backed down and decided to return the cattle it had confiscated to try to force payment.

FILE - The Malheur National Wildlife Refuge in Ore
A members of the group occupying the Malheur National Wildlife Refuge headquarters, walks to one of it's buildings, near Burns, Oregon, Jan. 4, 2016.

The federal government's land ownership has long been a contentious issue, particularly in the western part of the United States.  According to a report by the Congressional Research Service, federal agencies own 28 percent of the country's land, most of which is in the western states and Alaska.  

At 53 percent, the state of Oregon has the fifth-highest percentage of federally owned land.

The report cites early treaties and land settlement patterns for why so much of federal land is in the west.  The U.S. began with colonies on the east coast in the early 1600s through the country's independence from Britain in 1776.  It was not until the mid-1800s that the government acquired the land in the west.

The Malheur refuge is one of 560 in the United States set aside by the federal government to protect wildlife species and their habitats.

Watch video report from VOA's Zlatica Hoke: