Zimbabwe on Thursday announced a new round of power-sharing talks next week in South Africa, while accusing former UN chief Kofi Annan of trying to boost the opposition with a visit set for this weekend.

President Robert Mugabe and opposition leader Morgan Tsvangirai signed a power-sharing deal more than two months ago but have yet to form a unity government to end political turmoil after controversial presidential elections.

Under the deal, 84-year-old Mugabe would remain as president while Tsvangirai takes the new post of prime minister.

But their two parties have drafted conflicting versions of a constitutional amendment to lay out the new premier's powers. Neither side has released details of their proposals.

The government mouthpiece Herald newspaper said that the parties would meet next week with former South African president Thabo Mbeki, the regional mediator in the crisis, to resolve their differences.

The paper did not give any date for the talks, and Mbeki's spokesman Mukoni Ratshitanga could not confirm the meeting.

South African government spokesman Themba Maseko urged both sides to resolve their differences and begin tackling Zimbabwe's deepening humanitarian crisis.

"The government is disappointed to note that political interests have taken priority at the expense of the lives of ordinary Zimbabweans," Maseko told reporters after the weekly cabinet meeting.

"Cabinet is extremely concerned about the political impasse that is creating a humanitarian crisis in Zimbabwe," he added.

"South Africa calls on the leaders of Zimbabwe to take urgent steps to finalise the amendments to the constitution... without any further delay and before the situation of ordinary Zimbabweans degenerates any further," Maseko said.

Zimbabwe's economy has been in free-fall for years, leaving 80 percent of the population in poverty and nearly half the country in need of emergency food aid by January, according to the United Nations.

The country suffers the world's highest inflation rate, last estimated at 231 million percent in July.

A breakdown in water and sanitation has also sparked an outbreak of cholera that has killed 73 people in recent weeks.

Annan, the former UN secretary general, planned to visit to Zimbabwe this weekend to find ways of easing the humanitarian crisis, but the government Thursday rebuffed his effort as a "partisan mission" and asked him to defer it.

Annan said last Friday that he would travel to Zimbabwe with former US president Jimmy Carter and rights activist Graca Machel, wife of former South African president Nelson Mandela.

But the Herald newspaper accused the three, who belong to a group of senior statesman known as the Elders, of seeking to boost the MDC in power-sharing talks.

"The visit has been deemed a partisan mission by a group of people with partisan interests," an unnamed government source said in the paper.

"The Elders wrote to government on the intended visit, but they have been advised that while it appreciates the humanitarian concern by the group, it was important for them to plan their visit on a date that is convenient and agreed to by both sides," the source added.

Tsvangirai defeated Mugabe in the first round presidential election in March, but pulled out of a runoff in June, accusing the ruling party of coordinating deadly attacks against his supporters.

The power-sharing deal was meant to end the turmoil, but Mugabe has moved to unilaterally appoint cabinet ministers to the unity government.

Tsvangirai has refused to join the government until the parties reach an agreement on the cabinet and on his powers as the new prime minister.