BISMARCK, N.D. -Investigators say private security guards with dogs who were involved in a clash with Dakota Access pipeline protesters weren't licensed to do security work in North Dakota.

Morton County Sheriff's Capt. Jay Gruebele released a statement Wednesday saying results of his office's investigation have been forwarded to prosecutors for consideration of misdemeanor charges.

The clash occurred Sept. 3, after construction crews removed topsoil from private land that protesters believe contained Native American burial and cultural sites. The state and pipeline company dispute that any sacred grounds have been disturbed.

Authorities said four security guards and two guard dogs were injured. The Standing Rock Sioux tribe says protesters reported that six people were bitten by security dogs, and at least 30 people were pepper-sprayed.

The pipeline company didn't immediately respond to a request for comment Wednesday.