Denver Police in riot gear arrested 20 protesters near the steps of the Colorado Capitol on Saturday after a peaceful protest escalated into a clash when a group of 2,000 tried to advance up the Capitol steps.

Police said that they used pepper spray, and either rubber bullets or pepper balls, according to the Denver Post.

“Unfortunately at one point, that group did try to occupy the capital, which is illegal. We made sure that they knew that, it was pretty clear that they were not allowed to do that, they tried to do it anyway,” Denver police spokesman Matt Murray said, according to 9 News. “We had to step in and push them off. Things escalated; we did have to call out city-wide for assistance.”

A Denver police spokesman told the Associated Press that some protesters had received medical treatment on the scene, but no one had been taken to the hospital.