Winnie Madikileza-Mandela is a controversial figure

The ex-wife of Nelson Mandela was to attend the premiere of an opera about her life - called The Passion of Winnie- in the city of Toronto.

In 1991 she was convicted of kidnapping and being an accessory to murder.

Canadian authorities can refuse entry into the country on the grounds of a criminal record, although it is not clear that has happened in this case.

Her application was turned down a day before she was to arrive in Toronto, for a gala fundraising dinner.

The organisers, the arts group MusicaNoir, said they were devastated and do not know why her visa was withheld.

They said Mrs Madikizela-Mandela's daughter and two security guards did receive visas.

The decision was made by the Canadian High Commission in South Africa.

Canadian immigration officials in Ottawa have not given any reason why the visa application was denied.

MusicaNoir pointed out that Mrs Madikizela-Mandela was permitted to visit the United States two weeks ago to receive an award for her work with Aids organisations.

Known as one of South Africa's most famous anti-apartheid activists, Winnie Madikizela-Mandela is also a controversial figure.

A six-year prison sentence for kidnapping a young activist who was later murdered was suspended on appeal.

In 2003 she was found guilty on charges of fraud and theft.