PORTLAND, Ore. — Protesters returned to the streets of Portland, Oregon, following a dayslong pause largely due to poor air quality from wildfires on the West Coast.

Police declared an unlawful assembly Friday night in a neighborhood near a U.S. Immigration and Customs Enforcement building where protesters had marched, according to a police statement.

Demonstrators participated in criminal activity and threw items at officers, police said, leading to 11 arrests.

Photos show that smoke was used to clear the crowd, and it appeared that tear gas was deployed. Police initially tweeted that tear gas was on the list of crowd control agents if people did not disperse, but the tweet was later deleted, KOIN-TV reported. Another tweet was issued that didn't mention tear gas.

“No, we are required by law to make that warning," Portland Sgt. Kevin Allen told the television station when asked about the initial tweet. “PPB is still prevented from using tear gas.”

Less than two weeks ago the mayor of Portland ordered police to stop using tear gas for crowd control during the frequently violent protests that racked the city for more than three months after the police killing of George Floyd in Minneapolis.

Mayor Ted Wheeler, a Democrat, was tear gassed when he went to a demonstration against the presence of federal authorities dispatched to the city to protect federal property.

He said he still wants police to respond aggressively to prevent violence and vandalism. Hundreds of people have been arrested since the protests started in May.

Demonstrators had not gathered in the city since at least Sept. 9, when police and protesters clashed near City Hall. Wildfires have spewed dangerously dirty air across Oregon, California and Washington state, and sent haze across the country.

The protesters in Portland want city officials to slash the police budget and reallocate that money to Black residents and businesses. Some demonstrators are also demanding the resignation of Wheeler, a white man and the scion of a timber company fortune.

In clashes with police, some protesters have broken windows, set small fires, punctured police car tires, shined lasers in officers’ eyes and pelted them with rocks and frozen water bottles.

Police criticized Wheeler's move, saying in a statement that it could force them to employ potentially more dangerous crowd control measures to quell violent demonstrations.