The proposal on Zimbabwe emerged from nearly 12-hour summit called to push Mugabe, opposition leader Morgan Tsvangirai and Arthur Mutambara, head of a smaller opposition group, into the unity government they agreed to form more than a month ago.
Without a government, and without a breakthrough at the summit, Zimbabwe is without leaders to resolve a spiraling economic crisis.
Tsvangirai told reporters that his party disagreed "totally" with the recommendation from the Southern African Development Community summit that both he and Mugabe name ministers in charge of police and other functions of the Home Affairs Ministry.
The regional bloc left the details of how the co-ministers would work together to parties who have so far shown little trust in one another. Tsvangirai has insisted Mugabe surrender control of police officers accused of politically motivated attacks on the opposition.
"We will not be part of an arrangement we disagree with," Tsvangirai said.
Mugabe and his entourage left the summit without commenting.
Tomaz Salamao, the executive secretary of the regional bloc, said Mugabe had accepted the ministry sharing proposal. That raised the possibility Mugabe would take Sunday's developments in Johannesburg as a mandate to form a government without Tsvangirai.
After all, the final summit communique also directed that an "inclusive government be formed forthwith in Zimbabwe," and Tsvangirai is the holdout.
Mutambara said he went into the summit backing Tsvangirai's claim on the police ministry, but accepted the regional bloc's ruling. Mutambara said his faction would not join any government Mugabe might try to form without Tsvangirai because it would have no legitimacy.
Mutambara called on Tsvangirai to keep talking to regional leaders to try to find a solution.
Tsvangirai said he would turn to the United Nations and the African Union for help, but was not abandoning the regional body, which has been mediating the Zimbabwe crisis for a year.
After two disputed elections and a wave of state-sponsored political violence against opposition members, Mbeki persuaded the rivals to sign a power-sharing agreement in September.
Mugabe, in power since independence from Britain in 1980, was to remain president under the power-sharing deal, with Tsvangirai as prime minister.
The African leaders also grappled Sunday with a new humanitarian catastrophe in Congo, lamenting that war and political conflict are still blocking development in the world's poorest continent.
Congo's east has been engulfed in recent weeks in fighting involving rebels, government soldiers and pro-government militiamen. The world's largest U.N. peacekeeping contingent has been unable to protect civilians in eastern Congo.
South African President Kgalema Motlanthe opened Sunday's extraordinary summit with a call for a cease-fire so humanitarian aid can reach some of the 250,000 people displaced by the fighting.
The summit's final communique also said members of the regional bloc could, if it were determined necessary, send peacekeepers to bolster the U.N. force, and repeated calls by others in Africa for the U.N. to expand the peacekeepers' mandate.
The communique placed the blame for the fighting on the rebel leader.
Congolese President Joseph Kabila attended the Johannesburg meeting of the 15-nation regional bloc, with his delegation sitting next to Angola, a neighbor Kabila had asked last week for military help.
When asked by reporters whether numerous reports of Angolan forces fighting in Congo were true, Salomao said: "No. But if required, they will be on the ground soon."
A 1998-2002 war in Congo drew in Angola, Zimbabwe and other neighbors. The current violence has roots in the 1994 Rwandan genocide, during which hundreds of thousands of minority Tutsis were slaughtered by Hutu forces. Millions of Hutus fled to eastern Congo.
Today, Congo's army is fighting rebels loyal to Laurent Nkunda, a Congolese Tutsi who claims to be protecting his ethnic group from militant Rwandan Hutus.
