Zimbabwean President Emmerson Mnangagwa accused his main rival Nelson Chamisa on Sunday of striking a deal with former leader Robert Mugabe on the eve of an election and cast doubt on Chamisa's intentions of rebuilding the country.

Mnangagwa, who did not provide any evidence of his accusations, said in a Facebook post that voting for 40-year-old Chamisa was tantamount to bringing back Mugabe in disguise.

He made the comments after Mugabe said he would vote for the opposition in Monday's election.

"I cannot vote for those who have tormented me," the 94-year-old said in a rambling address, in a reference to Mnangagwa, who took office with the military's support. "I cannot vote for ZANU-PF," the ruling party he long controlled.

Many in Zimbabwe knew no other leader but Mugabe, who led the country for 37 years and since independence from white minority rule in 1980. What began with optimism crumbled into repression, alleged vote-rigging, intimidation of the opposition, violent land seizures from white farmers and years of international sanctions.

The country hopes that a credible vote on Monday could get those sanctions lifted and bring badly needed investment for a collapsed economy. Mnangagwa, a former Mugabe confidante, has tried to recast himself as a voice for reform, inviting back Western dozens of election observers and pledging a free and fair vote.