Police in the city of Portland said they fired crowd control munitions and tear gas on Wednesday night to break up a gathering of about 200 people who threw rocks, lit fires and vandalized a U.S. immigration agency building.
Law enforcement officials had declared a riot for a second successive night, calling a protest near the Immigration and Customs Enforcement (ICE) office an "unlawful assembly."
Federal officers fired pepper balls and set off a few smoke devices, the Oregonian newspaper reported earlier.
Protests against racism and police brutality have swept the United States since the death on May 25 of George Floyd, a 46-year-old African-American man, after a white police officer knelt on his neck for nearly nine minutes.
The Portland protests are among those that have erupted occasionally in arson and violence, with federal officers sent into the northwestern city repeatedly clashing with crowds targeting its federal courthouse.
Wednesday's protest began in the Elizabeth Caruthers Park before demonstrators marched toward the ICE building.
"All persons near SW Bancroft St and SW Bond Ave must disperse," police had said on Twitter, warning the marchers they faced arrest and the use of tear gas, crowd control agents and impact weapons if they did not comply.
Two arrests were made on charges of "interfering with a peace officer and disorderly conduct," police said in a statement. The arrested men were booked into the Multnomah County Detention Center.
Police officers sustained minor injuries, the statement added, without specifying how many were injured.
Police had also declared a riot on Tuesday after protesters lit fires, threw rocks and smashed windows at county government offices in another location, in violence that also led to two arrests and a minor injury for an officer.
U.S. Attorney General William Barr drew fire from Democratic lawmakers this month for sending federal officers to disperse protesters in the city
