Canada has denied entry to South African anti-apartheid leader Winnie Madikizela-Mandela, who was to speak at a gala fundraiser in Toronto, organizers said Tuesday.

"Ms. Madikizela-Mandela has been denied access by the federal government to enter Canada and will not be able to travel to Canada" to attend the event, said Carole Adriaans, director of the arts group MusicaNoir.

Madikizela-Mandela "was packed today and ready to travel to the airport with her daughter (Zindzi) when she was informed that her visa had been denied by the Canadian embassy in South Africa," she said, citing Madikizela-Mandela's office.

Marina Wilson, a spokeswoman for the immigration department, would not comment on the specific case, citing Canadian privacy laws, but said "anyone convicted of a serious crime would be deemed inadmissible to Canada."

Adriaans told AFP Madikizela-Mandela was "devastated" by the decision, having been in New York only two weeks ago to accept an award for her work with AIDS and the United Nations-affiliated Save Africa Concerts Foundation.

"A week ago, they went to the (Canadian) embassy and felt everything would be fine. Yesterday morning, I got a telephone call saying she was having visa problems and was denied entry into Canada," she said.

Her distress was echoed by Canadian opposition leaders who demanded an explanation from Prime Minister Stephen Harper's Conservative government.

"It's an embarrassment," said opposition Liberal leader Stephane Dion.

"There are far too many visas being denied to individuals who want to come to this country for a whole series of very positive and helpful purposes," said New Democrats leader Jack Layton. "The government's got some explaining to do."

Adriaans noted that Madikizela-Mandela's daughter and two security guards received visas and Canadian ministers had even praised Mandela in letters to organizers.

Madikizela-Mandela, 70, entered politics and Nelson Mandela's life at the start of the second treason trial that would see him jailed for a total of 27 years. Nelson Mandela later became South Africa's first post-apartheid president and a Nobel Peace Prize laureate.

Soon after their wedding in June 1958 she was arrested for an inciting speech, leading her husband to remark, proudly and prophetically: "I think I married trouble."

In the coming years, she was in and out of jail.

A six-year sentence for kidnapping a young activist who was murdered was suspended on appeal and in 1994 she was made a deputy minister in Nelson Mandela's government, but was later sacked for insubordination. She was also eased out of the top ranks of the ruling party.

In 1992, the couple announced their separation.

Organizers said the Toronto gala will go on, showing excerpts of an opera about Madikizela-Mandela's life called "The Passion of Winnie" that is to premiere in the city on Friday.

Meanwhile American actor LeVar Burton, who played Kunta Kinte in the 1977 award-winning television mini-series "Roots," has been invited to speak at the gala dinner, in Madikizela-Mandela's absence.

(c) 2007 APF.