Portland police declare riot after police association building set afire

Hopes that the departure of federal forces from Portland, Ore., would settle tensions evaporated this weekend, as local police were forced to declare a riot Saturday night after protesters set fire to a police union building.

A group of rioters broke into the Portland Police Association offices and set the fire, prompting police to act. Social media video showed smoke and flames arising from inside the building.

Portland police forced protesters away from the building and warned they would use flash bang devices, tear gas and arrests to clear the area. The Saturday night declaration came a day after several arrests were made Friday night during similar protesting.

Several hundred people had gathered outside the police union building before the violence started, some chanting "no good cops in a racist system."

The union offices are located a few miles from the federal courthouse where U.S. law officers tried to quell violent protests a few weeks earlier.

The federal forces left last week after Portland's mayor suggested they were exacerbating tensions with racial justice protests, but the violence has continued.