Grace Mugabe
Zimbabwe President Robert Mugabe, 90, with his wife Grace, 49.Reuters

The wife of Zimbabwe's dictator Robert Mugabe has claimed that the author of a book on the 90-year-old leader committed suicide as a direct consequence of her prayers that God punishes detractors of her husband's regime.

South African native journalist Heidi Holland died in 2012, four years after the publishing of her acclaimed portrait of the Zimbabwean president: Dinner with Mugabe.

Grace Mugabe, 49, told political supporters at rally in the village of Bindura, north of Harare, that Holland was found hanged weeks after she had cursed her.

"There was a white lady who wrote a book castigating President Robert Mugabe," the First Lady was quoted as saying by local newspaper NewsDay.

"I held the book and prayed to God to deal with her. She committed suicide a month later."

Dinner with Mugabe gave a critical insight on the Zimbabwean freedom fighter turned dictator, through a series of interviews with people who had intimate knowledge of him.

Born in Johannesburg to a British father and a Swiss mother, Holland grew up in Southern Rhodesia (now Zimbabwe), then a British colony, and worked as a reporter for numerous US and British papers.

Grace Mugabe is seen as an increasingly possible successor to her husband at the helm of Zimbabwe.

Last week, she threatened one of her main contenders, Vice-president Joice Mujuru, with expulsion from the ruling Zanu-PF party, signalling a growing power struggle over the succession to the old leader amid concerns overs his failing health.

Zimbabwe's First Lady drew public anger last month after she was awarded a PhD only two months after she enrolled at the University of Zimbabwe, where her husband is chancellor.