Mr Jackson has pleaded innocent

The star faces seven counts of lewd acts on a child under 14 and two counts of plying the boy with alcohol to seduce him. He denies all charges.

Superior Court Judge Clifford R Anderson also said the media would not be allowed advance notice of hearings.

He said the grand jury's right to secrecy outweighed public interest.

The judge said there was a "clash of rights" between the defendant, attorneys, grand jurors and the media.

Friday's ruling by Judge Anderson will allow Mr Jackson's attorneys to ask witnesses what they know of the case.

But they are not allowed to ask what the witnesses saw in the grand jury room, what questions they were asked and how they answered them.

'Protect identities'

During the hearing, news media attorney Theodore Boutrous criticised the secrecy surrounding the grand jury proceedings.

He said many grand jury witnesses had been sneaked into the building where the grand jury is meeting, sometimes covered in blankets to hide their identities.

"The government is not supposed to smuggle people in and out of court," Mr Boutrous said.

Prosecutor Gerald Franklin said such measures were necessary to protect the identities of witnesses.

A grand jury hears evidence in private and decides if a trial can go ahead.