The FBI has opened an investigation into video footage of a Los Angeles police officer repeatedly striking a suspect in the face during a struggle on a Hollywood street.

The footage, shot by a local resident and posted on YouTube.com three weeks ago, shows two officers holding down 24-year-old Williams Cardenas as they arrested him in August on a warrant for receiving stolen property.

As the struggling suspect yells, "I can't breathe", one of the officers punches him sharply several times in the face before they are able to handcuff him.

The issue of police brutality is especially sensitive in Los Angeles, which erupted in riots in 1992 after the acquittal of officers involved in the videotaped beating of the black motorist Rodney King the previous year.

The LAPD has also opened an investigation into the incident and the two officers involved, identified as Alexander Schlegel and Patrick Farrell, and both have been reassigned to administrative work,

"There’s no denying that the video is disturbing," William Bratton, the LAPD chief, told a press conference. "But as to whether the actions of the officers were appropriate in light of what they were experiencing and the totality of the circumstances is what the investigation will determine."

Authorities learnt of the video footage, before it was posted online, when the defence made it public on September 14 during Mr Cardenas’s preliminary hearing. The district attorney’s office is reviewing whether to continue with the Cardenas case, which is scheduled for trial next week.

According to a police document obtained by the Associated Press, the officer and his partner described repeated blows to the suspect’s face in their written arrest report, as well as efforts by the man to resist and their concern that the man might grab one of their guns.

Andre Birotte, the LAPD's independent watchdog, said that his office was informed of the arrest in October and was monitoring the investigations.

But a lawyer with the police union said that he welcomed the investigations and argued that the two officers acted well within their rights and department policy.

In particular, the officers appeared to use what are known as "distraction strikes," a tactic for subduing suspects, he said.

"This would have never happened if the suspect had surrendered as he is lawfully obligated to do," said Gary Ingumenson, independent counsel for the Los Angeles Police Protective League, which provides legal representation for officers.

A spokeswoman for the FBC said that the agency opened a federal civil rights inquiry yesterday after the three-month old incident came to its attention.

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