BILLINGS, Mont. (AP) — U.S. officials on Wednesday announced approval of a conservation group's proposal to expand bison grazing on prairies in north-central Montana as part of a vast nature reserve over objections from some ranchers and elected officials.

The decision allows the American Prairie group to graze bison on U.S. Bureau of Land Management property and to remove about 30 miles (48 kilometers) of fences so the animals can roam more freely.

The Bozeman-based group already has more than 800 bison on a mix of public and private land. Its long-term goal is to piece together a 5,000-square-mile (12,950-square-kilometer) expanse that would include the C.M. Russell National Wildlife Refuge and have thousands of bison and other wildlife.

Some cattle ranches have sold property to the group as it amasses land to create the reserve, but others have fiercely opposed the effort. The critics worry that bison will displace cattle and that their agriculture-dependent communities will be forever altered.

Republicans including Montana Attorney General Austin Knudsen and Gov. Greg Gianforte sharply criticized federal officials after American Prairie received preliminary approval for the reserve last August.

Knudsen said in a Wednesday statement that the administration of President Joe Biden ignored local opposition to the proposal. Knudsen said federal officials instead catered to “radicals" who want to transform part of Montana into a wildlife viewing area.

Bureau of Land Management officials said they approved the proposal in accordance with the law after finding that bison grazing would not have significant negative effects on the land.

BLM acting State Director Theresa Hanley said the decision would help achieve the agency's mission of keeping public lands in good condition.

Gianforte's office on Wednesday was reviewing the final decision, spokesperson Brooke Stroyke said.

The proposal covered about 108 square miles (280 square kilometers) south of the small community of Malta and will allow American Prairie to increase the size of its bison herd from 813 animals to about 1,000 by 2025, the group said.

“It took longer than it should have, and we’re not naive about the politics,” said reserve Vice President Pete Geddes. “This has been four years and hundreds of thousands of dollars in expenses for American Prairie — to do what any other rancher would have done in 60 or 90 days.”

American Prairie in 2019 had scaled back its original request to graze bison across more than 450 square miles (1,165 square kilometers) following opposition from ranchers.

Massive herds of bison migrated through the region until the animals were hunted to near-extinction in the 19th century.

Matthew Brown, The Associated Press