An anti-capitalist May Day march in Seattle turned violent on Friday when demonstrators threw rocks and wrenches at police, who responded by lobbing "flashbangs" and shooting pepper balls, according to police and media reports.
"This is no longer demonstration management, this has turned into a riot," Seattle Police Captain Chris Fowler said in a statement.
The Seattle Police Department said on its Twitter account that at least three officers were injured in the scuffle, and at least five people had been arrested. Two of the officers were taken to a Seattle hospital with serious injuries, the department said.
Footage uploaded on Twitter on Friday evening showed a frenetic scene as a row of bicycle police clad in riot gear threw the concussive devices into the crowd, sending many scattering.
Police said demonstrators had damaged at least two dozen vehicles and lit garbage on fire. Images on social media also showed demonstrators smashing store windows.
The Seattle Times newspaper said the protesters had gathered around 6 p.m. local time after a peaceful march on immigration.
Protesters annually assemble on May 1, marking International Labor Day, as a day to focus attention on labor and immigration issues. Demonstrators in cities across the country also used the occasion to rally against police violence.
In Baltimore, demonstrations were peaceful and even celebratory on Friday after prosecutors brought charges against all six officers involved in the arrest of Freddie Gray, the 25-year-old black man who died of spinal injuries suffered while in police custody earlier this month.
Gray's death has become the latest flashpoint in a national outcry over excessive force used against African-Americans and other minority groups by the white-dominated U.S. law enforcement establishment. It set off riots in Baltimore on Monday.
