Michael Jackson's representatives and record company are blocking the release of the singer's all-star 11 September charity single, according to the company that owns the rights.

Jackson enlisted Ricky Martin, Mariah Carey and 'N Sync to record What More Can I Give? in the weeks after the attacks on New York and Washington.

But the project stalled after it was revealed that the single's executive producer, F Marc Schaffel, has a past directing gay pornographic movies.

We are now totally perplexed and do not understand their motives at all

Yasumi Takeuchi Music Fighters

The Japanese company that now owns the rights to the song says Sony Music and Jackson's lawyer are trying to stop the project seeing the light of day.

The company, Music Fighters, bought the rights in the hope that it could release it around the first anniversary of the attacks, when it would also enlist Jackson for a charity mini-tour of Japan.

But Sony and Jackson's lawyer, Zia Modabber, seemed to be trying to block the release by refusing clearance for some of the artists involved, Yasumi Takeuchi, president of Music Fighters, said.

Dispute

"We are now totally perplexed and do not understand their motives at all," Mr Takeuchi said.

He added that Sony Music told Music Fighters that they would not be releasing the single because of an ongoing dispute with Jackson.

Sony and Ms Modabber should apologise to the artists who donated their time for a charity project, Mr Takeuchi said.

Jackson, who appeared in a 11 September benefit concert in October, has himself attacked Sony for refusing to release the track.

Bitter battle

But others believe Jackson's advisors urged Sony to drop the single without the singer's knowledge to avoid embarrassment about his connections with Schaffel.

It is the latest twist in a bitter battle between the star and his record company, which has seen Jackson accuse Sony chairman Tommy Mottola of being "racist" and "very, very, very devilish".

Another Jackson lawyer recently said the star was considering suing the record company for under-reporting sales of his latest album, Invincible, and other "Enron-like" accounting claims.

Invincible has sold two million copies in the United States - compared with 26 million copies of his 1982 classic Thriller.