WASHINGTON, April 3: Authorities have launched three investigations into police officers’ tactics in dispersing an immigration rally in Los Angeles earlier this week.

Rally organizers say police used excessive force, beating people with batons and firing as many as 240 rounds of rubber bullets into the crowd.

“This incident is one of the more disturbing and troubling in my 37-year career,” Police Chief William J. Bratton said on Thursday on CBS News' The Early Show.

News images showed police hitting a television cameraman to the ground, shoving people who were walking away from officers and injuries from the rubber bullets.

“I’m not seeking to defend it all. That’s why we’re having investigations. I’ve already indicated I don’t like what I see on the videos,” Mr Bratton said.

The investigations already under way include an overall departmental review of tactics, an internal affairs investigation into the behaviour of the officers and commanders on the scene, and an independent review by the Inspector General, the investigative arm of the Police Commission, which sets policy for the Police Department.

Rally organisers urged Los Angeles County District Attorney Steve Cooley to launch an independent investigation and denounced the police action as brutal.

“They were pushing children, elderly, mothers with their babies and beating up on the media" said Angela Sanbrano, an organiser.

The clashes started around 6pm Tuesday, 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.

A police order to disperse was in English and from a police helicopter, a likely ineffective tactic because of the noise and because many at the protest were Spanish-speakers, Mr Bratton said.

It appears to me, my early review, I have serious problems with the chain of command situation, serious problems with notification of the crowd to disperse, and very serious concerns that so many rounds, almost 240 rounds were fired. And no arrests made, he said.

Police union leaders urged against a "rush to judgment."

"Our officers gave a legal dispersal order and were met with violence. In the coming days it will become clear what transpired," said Los Angeles Police Protective League President Bob Baker in a statement. About 10 people were treated for minor injuries, though authorities expected the number to rise. Seven officers also received minor injuries.

John Mack, president of the five-member Police Commission, said he was "deeply disturbed and very disappointed" by the news 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.

He said police deliberately led troublemakers back to the peaceful marchers before beginning their assault.

“The only logical conclusion I can come to is that somebody wanted it to bleed into the march so that they can do some target practice on some of the immigrants that were marching," Nunez said.

News organisations also condemned the Police Department for its use of batons and riot guns against members of the media.

Chief Bratton promised to investigate the treatment of reporters.

“We should never be engaged in attacking anyone in the media," he said.