Portland police and partner law enforcement agencies fired pepper spray, pepper balls and a rubber ball grenade at masked antifascist protesters shortly after officers declared the demonstration an unlawful assembly Sunday in downtown Portland.

The extensive use of force follows months of police taking a different tack, allowing far-right activists and antifascist protesters to engage in small skirmishes on the streets without intervening.

Mayor Ted Wheeler and the Portland Police Bureau vowed a zero-tolerance policy on violence in anticipation of Sunday's demonstrations. Today, the mayor said police followed through on his expectations.

"We were clear about our expectations prior to Sunday and followed through on them," Wheeler says in a statement. "Our goal was to protect everyone's right to assemble while also protecting everyone's lives."

Activists and other observers have widely criticized the police on social media for tossing a rubber grenade into a crowd that mostly consisted of nonviolent protesters and journalists.

The violent clash between antifascist protesters and officers began around 1:15 p.m. and lasted for just under an hour. Police spokesman Sgt. Chris Burley says the bureau will review each use of force and evaluate whether the tactics were used properly.

The Portland Police Bureau has been strongly criticized by civil-liberties watchdogs for its crackdowns on leftist protesters this year. In February, the American Civil Liberties Union of Oregon called violent arrests of protesters "shameful." In June, the ACLU repeated its criticisms—and said the mass detainment of protesters and reporters was likely illegal.

As a group of mostly-masked antifascist protesters marched toward downtown, police tried to maintain a line between the hundreds of far-left activists and just over a dozen members of far-right group Patriot Prayer. But as the groups neared the intersection of 3rd Avenue and Salmon Street, the police line broke and at least one antifa protester landed a kick to a Patriot Prayer member, then ran away.

At the same time, some people in the crowd threw small rocks and water bottles at the far-right group. At the intersection, police arrested two protesters, wrestling them to the ground over their discarded bicycles. Portland police formed a circle around the officers making the arrests.

Protesters and journalists stood around the officers, watching and filming the arrests. At least one water bottle was thrown at the officers, and police say one officer was hit in the head with an unidentified projectile. A blue smoke bomb was set off near the police.

Burley says the officers asked the crowd to move back for two minutes and when the group refused to move, an officer threw a "rubber ball distraction device" into the crowd. The device is essentially a rubber grenade that spews rubber balls in all directions as it explodes with a loud boom and a flash of bright light.

Video footage of the incident shows a single protester throwing a stick at officers. One of the cops then tossed the rubber grenade into a crowd of people filming the police from several yards away. Although the grenade was likely thrown in response to the stick being launched at police, video shows the device landed next to someone who had not thrown anything at officers.

Journalists tweeted that the grenade landed within feet of where they were standing.

"It is our intent that whatever device is used is used to get the bad actors away from the police," Burley says. "I think one of the tactics that is used [by bad actors] is to intermingle with peaceful protesters and observers."

At the same intersection, while police were making arrests, a masked man dressed in black approached the police and appears to try to interfere with the arrest. An officer responded by pepper spraying him. The officer then appears to continue to pepper spray at least two people who did not approach the police line, including a photographer who was taking photos of the officer pepper spraying the protester.

Another video shot at the intersection shows an officer shove a legal observer with the National Lawyers Guild who was wearing a green cap that the group uses to identify themselves from protesters.

"One video does not paint a complete picture of what is occurring," Burley says. "These events are quickly evolving."

Burley says he cannot comment specifically on what threats officers were responding to when using force Sunday because their reports have not yet been reviewed.

Oregon State Police also fired pepper balls into the crowd after officers reported seeing projectiles thrown toward police, Burley says. The balls emit plumes of an irritant similar to pepper spray.

Portland police allege that some people in the demonstration threw "chemical irritants" at police, and that these irritants also affected other protesters nearby. Police accused protesters of similar tactics at a June 4 protest that was declared a riot in emails between Homeland Security officials and Portland Police.

Although the demonstration that started at the waterfront was declared an unlawful assembly, Burley says police did not extend the declaration to a rally and march organized by Portland Stands United Against Hate that took place nearby in Schrunk Plaza.

Police redirected those marchers, who had a permit, in an attempt to keep them safe and separate from the other demonstration, Burley says.