Los Angeles Police Chief William Bratton on Wednesday pledged to conduct an internal investigation to determine if police violated policy by using force to quell pro-immigration protesters.
Bratton said he had seen news footage showing a number of officers in riot gear striking protesters and some members of the media to the ground with batons, and others firing foam bullets into the crowd.
The incidents happened during a Tuesday rally in downtown Los Angeles.
"I regret and am, as are all of you, disturbed by the events so vividly depicted in the various news videos," Bratton told a press conference at the city hall.
"Police use of force in any context is always visibly and emotionally upsetting, even when necessary and lawful," the chief said.
"Our challenge in reviewing and investigating the actions of the police department ... and that of the public is to determine if that use of force was an appropriate response to the level of threat, disturbance and danger that they are encountering."
However, he is determined to meet the challenges, Bratton said.
The Los Angeles Police Department (LAPD) will create an "after-action report" to evaluate its handling of the event, and conduct a use-of-force investigation to determine if officers responded appropriately, he added.
Tuesday's rally by thousands of people calling for a path to citizenship for illegal immigrants was peaceful until about about 6 p.m., when police tried to disperse some demonstrators who had moved off the sidewalk into Alvarado Street in the downtown area.
Some demonstrators responded by throwing plastic bottles and rocks at officers, police said. Several dozen riot police, wearing helmets and carrying batons, fired a few dozen volleys of foam bullets into the crowd.
The clashes injured 15 police officers and at least 10 demonstrators.
The Radio and Television News Association (RTNA) said earlier that "there is evidence that officers knocked reporters to the ground, used batons on photographers and damaged cameras, possibly motivated by anger over journalists photographing efforts by officers to control the movements of marchers."