(Reuters) – A group of self-styled militiamen have occupied a US wildlife sanctuary headquarters in eastern Oregon in a dispute with authorities, officials and local media reports said on Sunday, in the latest row over federal land use in the West.

The occupation, which began on Saturday, followed a march in Burns, a small town about 50 miles (80 km) north of Malheur National Wildlife Refuge, to protest the detention of rancher Dwight Hammond Jr. and his son, Steven Hammond. The two were convicted in 2012 of setting fire to public land to protect their property from forest fires.

A federal court has ordered the Hammond family to be returned to prison after deciding their initial sentence was insufficient.

An unknown number of protesters occupied the building at the shelter’s headquarters in Princeton on Sunday, according to Jason Holm, a spokesman for the Fish and Wildlife Service and the Bureau of Land Management. There were no employees in the building, it said in a statement.

The militia leader said as many as 100 supporters were with them at the shelter, according to the Portland Oregonian newspaper.

Leaders of the occupation include Ammon Bundy, son of Cliven Bundy, owner of a ranch in Nevada where his family staged an armed protest against the Bureau of Land Management in April 2014, local media reported. The agency attempted to confiscate Bundy’s livestock after he refused to pay grazing fees. Federal agents eventually backed down, citing safety concerns, and returned hundreds of cattle to Bundy.

Bundy and his brother Ryan were among the Hammond family in the safe building, according to a report in the Oregonian.

“We want the government to abide by the Constitution… and play by the rules,” Ammon Bundy told CNN in a telephone interview on Sunday. Bundy said some of the occupiers were armed.

“We don’t have any intention to use force or be aggressive or commit any offence, but just as everyone has the right to defend themselves, that’s what it means – it means.”

On Saturday, Bundy told the Oregonian, “We actually plan to live here for many years.”

Federal and state authorities have not said how they plan to respond to the occupation.

“We will continue to monitor the situation for additional developments,” Fish and Wildlife Holm spokesman said in the statement. He did not immediately return phone calls seeking further details. No one answered calls to refugee phone numbers.

The shelter is in Harney County in rural southeastern Oregon, about 305 miles (490 km) southeast of Portland in the arid high desert in the east of the state.

In a statement issued late Saturday, Harney County Sheriff Dave Ward said several agencies were working to resolve the matter and he advised caution.

“For now, please stay out of the area,” Ward said. “Please maintain a peaceful and united front and allow us to overcome this situation.”

“The facility has become the instrument for carrying out all the tyranny that has been placed on the Hammonds,” the Oregonian quoted Ammon Bundy as saying, referring to the wildlife sanctuary’s headquarters.

“This was not a decision we made at the last minute,” Bundy added, asking other militia members to join them.

The Malheur National Wildlife Refuge, which covers 292 square miles (75,628 hectares), was established in 1908 by President Theodore Roosevelt as a breeding ground for the greater sandhill crane and other native birds. The headquarters complex includes a visitor center, museum and protection office.