Makoni said the talks could not yet be described as formal negotiations, but that he could confirm "that I know that there are communications between and among Zimbabwean leaders at various levels."
Mugabe may find it difficult to claim a mandate after a vote undermined by campaign violence, possibly making a coalition more palatable.
The idea of a coalition government has been raised previously, but the sticking point has long appeared to be ZANU-PF's insistence that Mugabe remain president of any unity government.
Opposition leader Morgan Tsvangirai has repeatedly pledged to bring moderate members of Mugabe's party into his administration, but not Mugabe.
Mugabe's Deputy Information Minister Bright Matonga said in a telephone interview Tuesday that a coalition "could be good for Zimbabwe."
"Whoever wins the presidential election will need the other parties to be able to govern," Matonga said. "We need each other."
But Matonga said he could not confirm reports the two parties were discussing sharing power. Opposition spokesman Nqobizitha Mlilo also said he could not comment on the reports that power-sharing talks were under way.
Tsvangirai beat Mugabe and two other candidates during the first round of presidential voting March 29, but official results did not give him the 50 percent plus one vote necessary to avoid a runoff set for June 27.
Mugabe's ZANU-PF lost control of Parliament for the first time since independence from Britain in 1980 in parliamentary voting held alongside the first round of presidential voting. Most seats went to candidates representing two factions of the Movement for Democratic Change that have since pledged to work together.
Independent human rights groups say opposition supporters have been beaten and killed by government and ruling party thugs to ensure the 84-year-old Mugabe, in power since independence from Britain in 1980, wins the second round.
The opposition says at least 60 of its supporters have been slain in the past two months. Zimbabwean government and party spokesmen repeatedly have denied the allegations.
Makoni said Tuesday that the violence since the first round would make it impossible for the planned June 27 runoff to be free and fair.
Mugabe and Tsvangirai "should be sitting across a table, discussing the future of Zimbabwe," Makoni said. "We ... implore them to agree to work together."
South African President Thabo Mbeki has mediated stop-and-start talks between Mugabe's and Tsvangirai's parties on behalf of the Southern African Development Community.
Mbeki has insisted on a media blackout, and his spokesman, Mukoni Ratshitanga, said the reports of renewed talks, which first appeared Tuesday in South Africa's respected Business Day newspaper, were untrue.
Mugabe was lauded early in his rule for campaigning for racial reconciliation and building the economy. But in recent years, he has been accused of holding onto power through fraud and intimidation, and trampling on political and human rights. Zimbabwe's collapsing economy was a major concern of voters during the first round of voting. People are going hungry in what was once the region's breadbasket, with the world's highest inflation rate putting staples out of reach.
The country's economic decline has been blamed on the collapse of the key agriculture sector after the seizures - often violent and at Mugabe's orders - of farmland from whites. Mugabe claimed the seizures begun in 2002 were to benefit poor blacks, but many of the farms went to his loyalists.
