BISMARCK, N.D. — A dozen law enforcement officials in North Dakota are imploring President Barack Obama in a letter to send federal officers to help local police during protests against the $3.8 billion Dakota Access oil pipeline, citing costs, fatigue and a growing fear of vigilante justice.

The officials asked Obama for 100 Border Patrol agents and members of the U.S. Marshals Service Special Operations Group, along with an unspecified amount of financial assistance, saying they've been "completely and utterly abandoned" by the federal government. The letter was dated Friday, and officials released details Monday.

"If we do not receive federal assistance, the safety and well-being of law enforcement officers, citizens of the community, and the protesters themselves are at grave risk," stated the letter spearheaded by Morton County Sheriff Kyle Kirchmeier.

Obama last month said his administration is monitoring the dispute surrounding the nearly finished four-state pipeline that's intended to carry North Dakota oil to a shipping point in Illinois. The White House didn't immediately respond to a request for comment Monday.

U.S. Customs and Border Protection did provide 11 Border Patrol agents to help with protest policing last month, according to the agency.

Nearly 575 pipeline opponents have been arrested since August in the Bismarck area and in the camp area on federal land along the pipeline route where thousands have been staying to oppose a project they believe threatens American Indian cultural sites and drinking water for the Standing Rock Sioux.

The camp has begun to thin out due to harsh weather and because the pipeline is stalled while developer Energy Transfer Partners and the Army battle in court over permission to cross under the Missouri River in North Dakota, but many vow to stay through the winter. The most recent arrest came Monday morning, when a protester crossed a barricade that law enforcement has set up on a closed bridge in the camp area, Morton County sheriff's spokesman Rob Keller said. Three others were arrested at the barricade last Thursday.

Law enforcement officials said they're also concerned that "community sentiment has turned volatile" after months of disruptions by protesters and they're worried that area residents will "take matters into their own hands." Bismarck police last Thursday arrested one of two men who were captured on video wearing masks and threatening protesters outside of a hotel on Dec. 5.