The head of the BALCO lab at the centre of a global steroid scandal said in an interview to be aired on Friday that he witnessed track star Marion Jones using steroids in a drug program he devised.

"After I instructed her how to do it and dialed it up, she did the injection with me sitting right there next to her -- right in front of me," Victor Conte told the ABC News magazine 20/20 in an interview released on Thursday.

Conte, who faces federal steroid distribution charges, said he started the programme for Jones prior to the 2000 Olympics and continued afterwards.

Jones has long said she never used steroids, although she has praised a zinc supplement Conte marketed.

"We invite the public to decide: Victor Conte is a man facing a 42-count federal indictment, while Marion Jones is one of America's most decorated female athletes," her attorney Richard Nichols said in a statement,

"Mr Conte's statements have been wildly contradictory, while Marion Jones has steadfastly maintained her position throughout: She has never, ever used performance enhancing drugs."

LEGAL ARENA

It is not clear why Conte chose to speak out at this time, especially since such statements are unlikely to help him in the legal arena. Conte has irked defence lawyers, who fear his statements could hurt his case at trial expected next year.

"I have no bone to pick with Marion. I'm here today because I believe that the world needs to hear the truth, the whole truth and nothing but the truth, so that we can really attempt collectively to try to genuinely create a level playing field for the athletes of the future," Conte said in the interview.

"Mr Conte chose to make unsubstantiated allegations on television, while Marion Jones demanded to take and then passed a lie detector examination," Nichols said.

"Mr Conte is simply not credible. We challenge him to submit to the same lie detector procedure that Marion Jones passed."

Last summer Conte's lawyer Robert Holley wrote to US President George Bush offering to name names in exchange for probation.

"George never did answer my letter," Holley told a pretrial court hearing on Wednesday.

The San Francisco Chronicle also reported on Thursday excerpts from closed-door grand jury testimony from New York Yankee Jason Giambi in which he admitted to using steroids.

A spokeswoman for the New York Yankees declined to comment.

Giambi had worked with Greg Anderson, personal trainer and long-time friend of baseball legend Barry Bonds.

Anderson is facing steroid distribution charges in the BALCO case along with Conte and two others and has admitted in court papers to himself using steroids.

Lawyers for the two most famous people who testified before the Grand Jury, track and field star Jones and San Francisco Giant Bonds, denied the athletes had used steroids.

The BALCO-related federal grand jury testimony is under court seal and prosecutors have declined to comment on their contents. A witness who does not tell the truth before the grand jury could face perjury charges and jail time.

The US Attorney's office issued an angry response to the leaks about Giambi, saying it would request a formal Department of Justice investigation into the leaks.

"Violations of grand jury secrecy rules will not be tolerated," United States Attorney Kevin Ryan said in a statement.