PORTLAND, Ore. (AP) — Police forced protesters away from a law enforcement building in Oregon's biggest city early Sunday, as efforts to stop the demonstrators from gathering at the building seemingly fell apart.

The protesters apparently had plans Saturday night to march from a park to the Penumbra Kelly public safety building, news outlets reported. But, a standoff between marchers and officers took place on a bridge along the way — and the demonstrators retreated.

Protesters appear to have returned to the park, and then taken cars to the building, according to a reporter for The Oregonian/Oregon Live.

Police initially declared an unlawful assembly, saying items had been thrown at officers, green lasers had been pointed at them and paintball guns had been fired.

The gathering was later declared a riot. Officers had been hit with rocks, bottles and other objects, police said.

Images posted online showed officers using smoke to clear the area. Several people were seen being detained, but it's unclear whether any arrests were made.

Similar protests have previously occurred at the Penumbra Kelly building, including last weekend.

The unrest followed rivaling protests Saturday afternoon. Federal authorities forced demonstrators away from a plaza near a federal building as dueling demonstrations by right-wing and left-wing protesters turned violent.

The area includes county and federal buildings and has been the site of numerous recent protests. Department of Homeland Security officers moved through the plaza across from an 18-story federal building. A federal courthouse is also near that area.

Violent demonstrations have gripped Portland for months, following the police killing of George Floyd in Minneapolis police custody.

The Saturday afternoon demonstration involving hundreds of people began about noon near the Multnomah County Justice Center, news outlets reported. Demonstrators hurled rocks and other items at each other and got into fights. Streets were blocked amid the mayhem.

Right-wing groups had announced a rally near the Justice Center Saturday afternoon that quickly drew counter demonstrators.

No arrests were reported.

In a statement, Portland Police said there had been questions about why the afternoon gathering wasn’t declared a riot and why city police officers didn’t intervene. Incident commanders have to determine whether police action will make things more dangerous, the statement said.

“In this case there were hundreds of individuals and many weapons within the groups and an extremely limited amount of police resources actually available to address such a crowd,” police said. “Additionally, (Portland police officers) have been the focus of over 80 days of violent actions directed at the police, which is a major consideration for determining if police resources are necessary to interject between two groups with individuals who appear to be willingly engaging in physical confrontations for short durations.”