PORTLAND, Ore. (AP) — Protesters in Portland hurled several firebombs at officers in Oregon’s largest city during a demonstration over a Kentucky grand jury’s decision to not indict officers in the fatal shooting of Breonna Taylor, police said, escalating tensions in a city that’s already seen nearly four months of nightly protests over racial injustice and police brutality.

Deputy Police Chief Chris Davis said Wednesday night’s demonstrations were the most violent that Portland has seen thus far in four months of nearly nightly unrest since the death of George Floyd, a Black man who died in Minnesota after a white officer held a knee to his neck. Multnomah County District Attorney Mike Schmidt — who has been criticized for dismissing cases against hundreds of protesters — condemned the violence and called for calm.

Thirteen people were arrested during the demonstration.

U.S. agents with the Federal Protective Service, who were guarding a federal courthouse nearby, offered assistance and the Portland police accepted because it was an “emergency need in the moment,” Davis said at a news conference Thursday.

“I can’t say that just because last night was exceptionally violent that that’s the beginning of a trend,” he said. “I certainly hope not.”

He added, “We’re at the mercy of people who show up … and what they intend to do.”

No tear gas was used by local or federal law enforcement, Davis said.

Schmidt said a peaceful protest intended to honor Taylor was sabotaged by violence.

“I am thankful that no Portland police officers or Portland firefighters were injured,” he wrote in a statement Thursday. “There is no justification for a person to ever throw an incendiary device, to set fire to buildings or to engage in other violent and destructive behavior.”

Those arrested included a 23-year-old man who was charged Thursday with riot and unlawful possession of a destructive device. A probable cause affidavit filed Thursday in court says a police officer saw Joseph Robert Sipe light the firebomb’s wick and throw it.

Sipe later said he had tossed the lighted device behind the police line as it advanced, according to the affidavit.

Sipe is identified in court papers as a homeless ex-Marine who has schizophrenia. His public defender, Grant Hartley, didn’t immediately return an email seeking comment.

Two other individuals were charged Thursday with squirting accelerant on barricaded doors at the police headquarters, throwing a firebomb that didn’t explode and throwing rocks at windows. The prosecutor said in a news release that an unidentified person dropped a backpack of rocks in the middle of the protest and people started throwing them.

The protesters Wednesday joined demonstrators around the U.S. who were enraged that a grand jury didn’t indict officers in the shooting of Taylor, a Black woman who was shot to death in her Louisville home by officers conducting a drug investigation.

Police said protesters hurled three firebombs — also known as Molotov cocktails — at officers and threw rocks that shattered windows at a law enforcement precinct station. One officer was hit in the foot by one of the firebombs and a fire department medic put out the flames.

Taylor, an emergency medical worker, was shot multiple times by white officers in Louisville who entered her home during a narcotics investigation in March.

The Kentucky grand jury returned three charges of wanton endangerment Wednesday against fired Louisville Officer Brett Hankison over shooting into a home next to Taylor’s with people inside.

In Portland, demonstrators have taken to the streets almost every night for four months to protest police brutality and to demand a reduction in police funding. A small number have frequently set fires, smashed windows and thrown objects at police.

More recently, protesters have targeted Portland Mayor Ted Wheeler for allowing police to use tear gas to disperse crowds and for what protesters believe are overly aggressive tactics.

Wheeler banned all use of tear gas last week.

At the same time, the mayor has become a frequent focus of attacks from President Donald Trump, who has accused him of being weak and doing nothing to stop the unrest in his city.

The right-wing group Proud Boys plans a rally in Portland this Saturday to support Trump and the police and to condemn anti-fascists, what the group calls “domestic terrorism” and Wheeler’s leadership, according to their permit application.

The city denied the permit, citing the estimated crowd size of 10,000 during a pandemic, but police said Thursday they will not try to stop the Proud Boys from gathering at a park in north Portland.