Protesters repeatedly set fire late Monday night to a police union headquarters building and were repelled by officers spraying tear gas, officials said. Twenty-five people were arrested amid clashes that stretched into Tuesday morning.

People in a group of about 300 people hurled rocks and bottles at officers and set three fires to the sides of the building and one to an awning, police said. All the fires were put out.

One demonstrator climbed atop the building’s roof to unfurl a banner and the building’s walls were spray-painted, The Oregonian/OregonLive reported.

Portland has been gripped by nightly protests for nearly three months since the police killing of George Floyd in Minneapolis. Demonstrations, often violent, have targeted police buildings and federal buildings. Some protesters have called for reductions in police budgets while the city’s mayor and some people in the Black community have decried the violence, saying it is counterproductive.

Before dawn Monday, police used tear gas to scatter demonstrators who hurled rocks, bottles and commercial-grade fireworks at officers and set fires in the streets as they marched on a precinct station. Twenty-three people were arrested.

During that demonstration, a group of about 200 lit a dumpster on fire and used it as a shield as they approached the station, police said. They threw objects at officers, hitting some positioned on the roof, and lit an awning on fire. One officer suffered a wrist injury after he was hit with a piece of ceramic.

The FBI said Monday that a threat last week that prompted the closure of a federal courthouse and other federal buildings did not appear to be credible.

Among the buildings closed was the Mark O. Hatfield U.S. Courthouse, which was a target of protesters who repeatedly clashed in July with federal agents.

(AP)