An ally of Vice President Joice Mujuru who was recently ousted from his post as ruling party spokesman said the allegations that he conspired against Mugabe are false.
Rugare Gumbo, the ousted spokesman, was identified in The Sunday Mail as a plotter against Mugabe, who has been in power since independence in 1980.
The Sunday Mail cited a voice recording and reported comments as evidence of the alleged plot but it did not attribute the information to security officials or other sources.
Grace Mugabe has assumed an increasingly political role, angering some party insiders who believe she does not have leadership credentials in a country struggling with high unemployment and other social problems.
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Gumbo said Robert Mugabe lambasted him during a meeting of senior leaders of the ruling ZANU-PF party on Thursday night.
"We were accused of attempting to overthrow the president and it was the president himself who led the charges," Zimbabwe's Daily News quoted Gumbo as saying. "He says 'we have done wrong and should leave the party,' but this is just a smear campaign to eliminate people who are standing by the vice president."
Mugabe has often accused foreign powers, particularly Britain and the United States, of trying to undermine him. Western leaders have criticized Mugabe's human rights record.