"Some war is going on in my party. People want positions. They even want to push senior people out," Mugabe said in a speech delivered to lawmakers yesterday but broadcast on national television today.
"Some are saying 'Mr Mugabe is old so he should step down'. Me, who brought the party to where it is now, who experienced colonial rule, jail and was in the bush alongside the freedom fighters?
"Then along comes a mere child. No! when my time comes I will tell you," he said withoit naming anyone.
Grace Mugabe called on Mujuru to resign or be forced to step aside.
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Mujuru and powerful Justice Minister Emmerson Mnangagwa are seen as the leading contenders to replace the 90-year-old Mugabe, who has been in power since independence from Britain in 1980.
The battle escalated following Grace Mugabe's surprise nomination to lead the powerful women's wing of ZANU-PF, amid speculation that she could be aiming to take over from her husband when he steps down or dies.