Jackson has pleaded innocent to child molestation charges involving another alleged victim in Santa Barbara County. Jackson attorney Benjamin Brafman said he was unaware of the Los Angeles Police Department investigation.
"We have never been informed by the LAPD of any investigation that they are conducting of Michael Jackson," he said. "I would point out that since I have been involved in this case I have addressed literally dozens of completely baseless rumors on a daily basis, and this appears to be just another one of them."
The Los Angeles County district attorney's office asked the LAPD to investigate the new allegation a month ago, said Mary Grady, commander of the department's public information office.
"The victim alleges the acts took place in the city of Los Angeles in the late 1980s," she said.
The allegations are being investigated by the Child Protective Section of the department's Juvenile Division. Grady declined to elaborate on such details as the age or sex of the alleged victim.
Los Angeles district attorney's spokeswoman Sandi Gibbons declined comment.
"This is a matter under investigation by the LAPD," she said. "We are not the investigative agency."
Santa Barbara County prosecutors did not immediately return calls for comment Tuesday evening.
Steve Cron, a defense attorney who has represented clients accused of molestation, said the new alleged abuse would be within the statute of limitations if it occurred after 1988. He said the accuser could also help prosecutors in the Santa Barbara case show a pattern of abuse, though the amount of time since the alleged acts could hurt the accuser's credibility.
"The questions are asked: Why didn't this allegation surface earlier? Why didn't he report it to someone a long time ago? How accurate is his recollection? How accurate is his ability to relay the events to someone else?" Cron said.
Also Tuesday, an appeals court rejected a request by several news agencies to lift a gag order placed on the parties by the judge in the Santa Barbara case.
An attorney representing news organizations, including The Associated Press, said in a filing last week before the state Court of Appeals that the order imposed unconstitutional "prior restraint" on attorneys and potential witnesses. He asked that it be immediately lifted.
Jackson and his attorneys also oppose the order on grounds that it blocks their ability to address false rumors and news reports.
At a hearing earlier this month, the judge made what he said was a final change to the policy: He said attorneys wishing to respond to news reports could submit to him in writing what they wanted to release, and that he would rule on whether the statements violated the gag order.
Jackson was charged by the Santa Barbara district attorney late last year with committing lewd or lascivious acts upon a child and administering an intoxicating agent to the child. Jackson has pleaded innocent. A pretrial hearing is scheduled for April 30.
The pop singer reportedly reached a multimillion-dollar settlement with a boy who accused him of molestation in 1993. No criminal charges were brought in that case.