Pop star Michael Jackson is again at the centre of a police investigation. About 20 officers searched his California ranch on Tuesday as part of an ongoing but undisclosed criminal investigation. Jackson was not home.

Cable channel Court TV said the investigation stems from allegations of sexual abuse brought by a 12-year-old boy against the 45-year-old Jackson.

Up to 70 investigators from the Santa Barbara County sheriff's and district attorney's offices entered Jackson's sprawling Neverland Ranch outside of Santa Barbara on Tuesday morning. No immediate arrests were made.

Court TV reporter Diane Dimond, who is on the scene, says a source told her that police not only had a search warrant, but an arrest warrant. Dimond told CNN's Larry King that had Jackson been at the ranch, the warrant would have been executed.

Jackson's spokesman, Stuart Backerman, said the singer was not at his ranch but was with his three young children in Las Vegas filming a music video.

"We cannot comment on law enforcement's investigation because we do not yet know what it is about. Michael will, as always, cooperate fully with authorities in any investigation," the Backerman statement said.

Jackson denounced media coverage of the search in a statement released by Backerman to The Associated Press.

"I've seen lawyers who don't represent me and spokespeople who do not know me speaking for me. These characters always seem to surface with dreadful allegations just as another project, an album, a video is being released," the Jackson statement said.

The search came on the same day Epic Records released Number Ones, a greatest hits collection featuring Jackson's new single, One More Chance.

Nine years ago, a 14-year-old reached an out-of-court agreement to settle a lawsuit accusing the singer of molesting him in 1992. No criminal charges were ever brought and Jackson has maintained his innocence.

Police dropped an investigation into the case after the settlement was reached and the boy made it clear that he would not participate in any criminal prosecution of the pop star.

In February, Jackson revealed in a British television documentary that he shared his Neverland bedroom with young boys and made his children wear masks in public.

"Why can't you share your bed? It's the most loving thing to share your bed with somebody," Jackson said.

The frank revelations sparked calls for an investigation by California child welfare authorities at the Neverland ranch, where Jackson has built theme-park style rides, a zoo and a mini railroad track which he throws open to local children.

In June, Jackson settled a $12 million US breach of contract lawsuit by his former top adviser, avoiding a trial that threatened to spill details of his personal life into open court.

Jackson is also connected to Hollywood private eye Anthony Pellicano, who began serving federal prison time Monday for possessing illegal explosives.

Pellicano worked for Jackson, through his legal team, during the 1993-94 police investigation into child abuse accusations.

Pellicano is under investigation on suspicion that he secretly and illegally wiretapped the conversations of celebrities and their lawyers.

Dimond told the New York Post that she was contacted by the FBI last week. She said agents informed her that her phone was monitored by Pellicano back in 1994, while she was working as a reporter for Hard Copy and covering accusations by a young boy that he was molested by Jackson.

The New York Times reported last weekend that the Pellicano investigation is widening. Managers, actors, businessmen and lawyers are being questioned, and in some cases subpoenaed, by the federal government.

On Nov. 26, CBS is scheduled to air a Jackson special consisting mainly of old concert footage.