Harare - Zimbabwean Vice President Emmerson Mnangagwa appears to have fallen from favour and is no longer viewed as a likely successor to President Robert Mugabe, 93, deepening the mystery over who will take over from a man who has ruled since independence in 1980. Mugabe has led attacks on his old friend, reflecting turmoil within the ruling Zanu-PF party and adding political uncertainty to the problem of a deteriorating economy that is increasing hardship for many Zimbabweans. Mnangagwa on Thursday fought back against allegations by his co-deputy that he lied about being poisoned, in a row that displays the growing political in-fighting ahead of next year's election. He was accused by fellow vice president Phelekezela Mphoko of undermining President Mugabe by claiming to have been poisoned during a ruling Zanu-PF rally in August. ALSO READ: Mugabe no longer in charge - opposition "I never said I was poisoned in Gwanda, but that I fell ill," he said accusing Mphoko of "subjective falsehoods and mischievous perceptions". "My commitment to national unity, peace and stability is undoubted and unquestionable," he added, dismissing Mphoko's claim that he was attempting to undermine Mugabe's authority. "I have an impeccable history of unflinching loyalty to the party, and his excellency the president, comrade Robert Gabriel Mugabe and have never acted in a manner that undermines his authority or the stability of Zimbabwe."First Lady Grace Mugabe in a scathing attack told Mnangagwa:"When you go around saying all nonsensical stuff, it means you have failed in politics."