May Day demonstrations turned violent in Seattle on Friday night as protesters clashed with police.
At least three officers were injured, and an "explosive device" was thrown at police during demonstrations, according to the Seattle Police Department's verified Twitter account. A total of 15 people were arrested, police said.
"This is no longer demonstration management, this has turned into a riot," said Capt. Chris Fowler, according to the department's Twitter.
Two of the three officers hurt during the demonstrations were taken to Harborview Medical Center "with serious injuries." Police used pepper spray and pepper balls once people in the crowd began throwing rocks and wrenches at officers, according to the account.
Several people had been arrested and 25 vehicles had been damaged by 8:30 p.m., police said on Twitter.
The clash subsided by 9:30 p.m., according to TV news reports.
Police did not return calls for additional information.
About 9:40 p.m., Seattle Mayor Ed Murray said in a statement that the evening's events were unacceptable.
"Tonight we saw assaults on police officers and senseless property damage, which cannot be tolerated," the statement said. "Those who are violent will be arrested. We will work to disperse groups that are threatening the safety of our residents and businesses."
At least one Portland police officer was assaulted and injured as an increasingly unruly crowd threw objects and chairs at officers, the Associated Press reported.
Hundreds of protesters were reported in the evening crowd, according to the AP.