Los Angeles ? Police Chief William J. Bratton on Wednesday promised an investigation into the conduct of police who dispersed an immigration rally, after videos captured officers using force with reporters and firing rubber bullets into crowds.

Bratton said officers fired 240 “nonlethal” rounds to clear MacArthur Park late Tuesday. News images showed police pushing a television cameraman to the ground, shoving people who were walking away from officers, and injuries from the rubber bullets, including a Hispanic man with welts on his abdomen and back. Lines of officers moved through the park firing the rubber rounds.

“The events of yesterday, with all (the training) that we do, should not have occurred,” Bratton said at a tense news conference. “We should not be engaged in attacks on the media.”

John Mack – president of the five-member Police Commission, which sets policy for the Police Department – said he was “deeply disturbed and very disappointed” by the images.

“This was not a pretty picture. This incident raises serious concern regarding the use of force by some individual officers,” said Mack, who is one of Bratton’s bosses. The civilian commission has opened its own investigation.

Bratton said the clash occurred over 45 minutes to an hour as the rally wound down. Police were initially trying to deal with 50 to 100 “agitators,” he said.

“The individuals were there to provoke police,” Bratton said. “Unfortunately, they got what they came for.”

Rally organizers and reporters said the clashes started around 6 p.m., when police tried to disperse demonstrators who moved into a street. Authorities said several people threw rocks and bottles at officers, who used batons to push the crowd back to the sidewalk and then cleared the park.

Eight adults and a minor were arrested on charges ranging from public alcohol consumption to assault with a deadly weapon for throwing a rock at a police officer, Bratton said.

Seven officers suffered minor injuries, and another was pushed off his motorcycle, he said. About 10 people were treated for minor injuries, though authorities expected the number to rise.