Zimbabwe's President, Emmerson Mnangagwa, has 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 forced from power last year.
The army intervened to oppose Mrs Mugabe's attempt to succeed her husband as the country's leader, and the ruling Zanu-PF party then sacked Mr Mugabe, replacing him with Mr Mnangagwa.
An exiled member of the G40 group, former government minister Jonathan Moyo, has denied Mr Mnangagwa's accusation, tweeting that the blast "smacks of an inside job".
He was referring to an apparent power struggle between Mr Mnangagwa and his deputy, Constantino Chiwenga, the former army chief who forced Mr Mugabe out.
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.
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