The President of Zimbabwe, Emmerson Mnangagwa, said he suspects a group linked to the former first lady was behind an attempt on his life.
Two people died and more than 40 were hurt in an explosion near Mr Mnangagwa at a rally in Bulawayo on Saturday.
Mr Mnangagwa told the BBC's Fergal Keane that he suspected the G40 group, which supported Grace Mugabe for the presidency, had carried out the attack.
Mrs Mugabe's husband, Robert Mugabe, was removed from power last year.
Widespread suspicion that Mrs Mugabe intended to succeed her husband as the country's leader was a contributing factor to the political transition, and the army's involvement in it.
Mr Mnangagwa did not accuse Mrs Mugabe of being involved in the attempt on his life. He told the BBC he expects arrests to be made shortly.
"I don't know whether it was one individual - I would think it is broader than one person. I would think this is a political action by some aggrieved persons," he said.
Mr Mnangagwa, then vice-president, and Mrs Mugabe were the two main candidates to succeed the aging Robert Mugabe as president.
The faction supporting Mrs Mugabe was known as Generation 40 or G40.
Mr Mnangagwa described Mrs Mugabe as someone who had frequently insulted him in the past.
"On what basis would I trust someone who was used by a cabal to say things that had no basis," he said.
Despite the apparent attempt on his life, Mr Mnangagwa said Zimbabwe was stable and that foreign investors should not worry.
There would be no countrywide security clampdown and elections scheduled for next month would go ahead in a free and fair manner, he said.