BISMARCK, N.D. (AP) — A protest of a four-state, $3.8 billion oil pipeline turned violent after tribal officials say construction crews destroyed American Indian burial and cultural sites on private land in southern North Dakota.

Morton County Sheriff's Office spokeswoman Donnell Preskey said four private security guards and two guard dogs were injured after several hundred protesters confronted construction crews Saturday afternoon at the Dakota Access pipeline construction site just outside the Standing Rock Sioux reservation. One of the security officers was taken to a Bismarck hospital for undisclosed injuries. The two guard dogs were taken to a Bismarck veterinary clinic, Preskey said.

Tribe spokesman Steve Sitting Bear said protesters reported that six people had been bitten by security dogs, including a young child. At least 30 people were pepper-sprayed, he said. Preskey said law enforcement authorities had no reports of protesters being injured.

There were no law enforcement personnel at the site when the incident occurred, Preskey said. The crowd dispersed when officers arrived and no one was arrested, she said.

Vicki Granado, a spokeswoman for Dallas-based Energy Transfer Partners, which is developing the pipeline, said the protesters broke through a fence and "attacked" the workers.

The incident occurred within half a mile of an encampment where hundreds of people have gathered to join the tribe's protest of the oil pipeline, which is slated to cross the Dakotas and Iowa to Illinois.

The Standing Rock Sioux have gone to court to challenge the Army Corps of Engineers' decision to grant permits for the project, and a federal judge will rule before Sept. 9 on whether construction can be halted.

The tribe fears the pipeline will disturb sacred sites and impact drinking water for thousands of tribal members on the reservation and millions farther downstream.

The protest Saturday came one day after the tribe filed court papers saying it found several sites of "significant cultural and historic value" along the pipeline's path.

Tribal preservation officer Tim Mentz said in court documents that the tribe was only recently allowed to survey private land, where researchers found burials, rock piles called cairns and other sites of historic significance to Native Americans.

Standing Rock Sioux Chairman David Archambault II said in a statement that construction crews removed topsoil across an area about 150 feet wide stretching for 2 miles.

"This demolition is devastating," Archambault said. "These grounds are the resting places of our ancestors. The ancient cairns and stone prayer rings there cannot be replaced. In one day, our sacred land has been turned into hollow ground."

Preskey said the company filmed the confrontation by helicopter and turned the video over to authorities. Protesters also have posted some of the confrontation on social media.

Morton County Sheriff Kyle Kirchmeier said in a statement that "individuals crossed onto private property and accosted private security officers with wooden posts and flag poles."

"Any suggestion that today's event was a peaceful protest, is false," his statement said.