Morgan Tsvangirai outlined his proposal for resolving the contentious issue of who would lead any unity government in a speech to regional Cabinet ministers gathered for a Southern African Development Community summit.

Tsvangirai's proposal, which he said his Movement for Democratic Change has presented in deadlocked negotiations with Mugabe's Zanu-PF party, would mean a major curbing of the powers Mugabe has wielded since the country gained independence in 1980.

But it also would leave Tsvangirai working closely with a leader he has reviled as a brutal dictator.

South African President Thabo Mbeki, who has been mediating Zimbabwe's power-sharing talks, spent much of the past week in Zimbabwe trying to push Mugabe and Tsvangirai to strike a deal. The question of Mugabe's role has been a major sticking point, with the longtime president reportedly refusing to yield any power and his administration publicly mocking Tsvangirai's claim to have the mandate to lead Zimbabwe.

In his speech to southern African leaders on Friday, the details of which were only revealed publicly last night, Tsvangirai said the two sides remained unable to agree on how powers would be divided between him and Mugabe. A South African Cabinet minister closely involved in the talks, Sydney Mufamadi, said yesterday that a deal was close but was unclear if a breakthrough would come during the summit.

Tsvangirai had walked out of talks in Harare on Tuesday, but his chief negotiator said yesterday that the negotiations were back on track. "We're talking here," Tendai Biti said after attending the opening session of the SADC summit.

On Friday, Tsvangirai said compromise was necessary because Zimbabweans would reject a deal "if any party is greedy. We have agreed that Mr Mugabe will be president whilst I become prime minister," he told the SADC ministers. "We envisage that the prime minister must chair the Cabinet and be responsible for the formulation, execution and administration of government business including appointing and dismissing his ministers. A prime minister cannot be given responsibility without authority and be expected to deliver."

Tsvangirai, whose party won the most seats in parliament in March elections, proposes that the president have no power to veto laws. The opposition also proposes that the president "shall be commander in chief of the defence forces of Zimbabwe," but exercise that power in consultation with the prime minister.

Tsvangirai came first in a field of four in the first round of presidential voting in March, but did not win by the margin necessary to avoid a run-off against second-place finisher Mugabe. Tsvangirai withdrew from the June 27 run-off because of attacks on his supporters blamed on Mugabe's party militants and security forces.

Mugabe held the run-off, and was declared the overwhelming winner, though the exercise was widely denounced.

Yesterday, Tsvangirai sat just behind Cabinet ministers from the region during the opening session of the summit, while Mugabe sat at the front table with other heads of state.

British Foreign Secretary David Miliband said in a statement from London that the summit offers Africans an important opportunity to support the power-sharing negotiations, adding: "The outside world continues to watch developments in Zimbabwe closely and with concern, not least given the deteriorating humanitarian situation."

The South Africans, appointed mediators by SADC, helped guide Mugabe and Tsvangirai to sign a memorandum of understanding on July 21 establishing a framework for negotiations. Mbeki praised that agreement yesterday and said the SADC would continue working "to help put Zimbabwe on the right road to its recovery."

Mbeki has insisted on quiet diplomacy. Some have portrayed his refusal to publicly condemn Mugabe as appeasement. Botswana President Seretse Ian Khama refused to attend the summit to protest Mugabe's welcome as a head of state. President Levy Mwanawasa of Zambia also has been sharply critical of Mugabe.