Supermodel agrees to give evidence at war crimes trial

Campbell had initially refused to speak to prosecutors over claims she was given "rough diamonds" by Taylor shortly after he became president in 1997, during a celebrity-packed reception held in South Africa by Nelson Mandela.

Taylor faces an 11-count indictment for crimes against humanity in the trial, which began at the International Criminal Court in The Hague but was then moved to nearby Leidschendam.

The Special Court for Sierra Leone issued an order giving Campbell an ultimatum to testify on July 29 at 9am "or to show good cause why you cannot comply with this subpoena".

Refusal could have led to prosecution for contempt, which carries a maximum seven-year prison sentence and a fine of about 342, according to the subpoena released by the court.

The spokeswoman said: "Naomi Campbell has confirmed she will attend the Charles Taylor trial at The Hague as per the court's request.

"She is a witness who has been asked to help clarify events in 1997.

"Miss Campbell has made it clear that she is willing to help the due process of law.

"For avoidance of doubt she is not being accused of any wrongdoing and is not on trial."

A spokesman for the Special Court for Sierra Leone previously said Campbell denied being given such diamonds, contrary to claims by actress Mia Farrow who is also due to give evidence.

Farrow gave a written statement to the court that Campbell told her about the gift but the judges refused to accept the statement when the prosecution tried to introduce it as evidence last January. Under cross-examination, Taylor said the story was "totally incorrect."

It is alleged Taylor had a role in the brutal civil war in Sierra Leone by supporting rebels there.

He denies all the charges against him.

The trial started on January 7 2008 and a judgment may not take place until early next year.