MANDAN, N.D. — Authorities say people protesting the construction of an oil pipeline in North Dakota gathered Tuesday at two construction sites on private property.

The Morton County sheriff’s office says about 300 protesters gathered along with 100 cars and a dozen horses at a construction site for the Dakota Access pipeline around 2 p.m. The state’s Bureau of Criminal Investigation is looking into reports of a possible assault on a construction worker and reports of protesters blocking workers from leaving the site and chasing them on horseback.

Protesters later gathered for about an hour at another construction site.

The sheriff’s office says no one was arrested during the either protest, but five people were taken into custody on disorderly conduct and other charges after temporarily blocking a highway.