ATLANTA — Protests took a violent turn in several U.S. cities over the weekend with demonstrators squaring off against federal agents outside a courthouse in Portland, Ore., forcing police in Seattle to retreat into a station house and setting fire to vehicles in California and Virginia.

A protest against police violence in Austin, Texas, turned deadly when police said a protester was shot and killed by a person who drove through a crowd of marchers. And someone was shot and wounded in Aurora, Colo., after a car drove through a protest there, authorities said.

The unrest Saturday and early Sunday stemmed from the weeks of protests over racial injustice and the police treatment of people of color that flared up after the May 25 death of George Floyd in Minneapolis.

In Seattle, police officers retreated into a precinct station early Sunday, hours after large demonstrations.

In Portland, thousands gathered Saturday for another night of protests over Floyd’s death and the presence of federal agents recently sent to the city by President Donald Trump.

In Richmond, Va., a dump truck was torched as protesters and police faced off late Saturday during a demonstration of support for the protesters in Portland.

Protesters in Oakland, Calif., set fire to a courthouse and damaged a police station Saturday evening.