Former South African president Thabo Mbeki has little leverage to push Zimbabwe's feuding parties to agreement, having lost his clout as leader of the region's most powerful state, analysts say.

Mbeki flew back to Zimbabwe to meet President Robert Mugabe and his main political rival and prime minister designate Morgan Tsvangirai to rescue the country's increasingly vulnerable power-sharing deal.

The two sides failed to reach a deal after more than seven hours of negotiations Tuesday, but were set to hold further discussions on Wednesday.

The much-anticipated agreement was brokered by Mbeki one month ago but has stagnated amid a deadlock over key cabinet posts, raising fears of a hollow victory in his bid to end Zimbabwe's economic and political crises.

The stand-off intensified this week as Mugabe awarded his ruling ZANU-PF disputed ministries and appointed two vice-presidents, leading to opposition threats to pull out of the pact and calls for Mbeki's return to break the impasse.

But analysts say Mbeki's chances for successful mediation are much slimmer since he was ousted as South African president by his own party last month.

As an ordinary citizen, Mbeki no longer has the leverage to pressure Mugabe to loosen his iron-fisted control after nearly 30 years in power, said Moeletsi Mbeki, a respected political analyst and the ex-president's brother.

"I don't think that our former president really has any leverage over Mugabe, which is why Mugabe proceeded to nominate his cabinet ministers before he even got there to mediate," he said.

The mere need for Mbeki's presence in Zimbabwe raised concerns about the success of the fragile political partnership, said Karin Alexander of the Institute for Democracy in South Africa.

"Having to have a mediator now suggests that this deal is unlikely to continue for terribly long because they need a mediator to go back every time there is a decision to be made. So I think that raises huge concern around the deal itself," she said.

Mbeki's continued role as mediator is also of concern as he no longer has tools in hand to negotiate an agreement, she said, noting that South Africa's government controls the flow of crucial supplies, including fuel needed in Zimbabwe's shattered economy.

Long vilified for his "quiet diplomacy," Mbeki faced increasing pressure at home and abroad to find a solution to Zimbabwe's problems as the regionally appointed mediator.

Moeletsi Mbeki, a frequent critic of his brother, pointed fingers at both the Southern African Development Community and South Africa's ruling African National Congress (ANC) for Zimbabwe's problems.

The regional bloc was "party to creating the Mugabe monster" while the ANC had given "a lot of comfort to the Mugabe regime," he said.

As the rival parties bicker, Zimbabwe's people face a daily struggle to survive against desperate food shortages and the highest inflation in the world, estimated at 231 million percent in July -- a tragedy sometimes lost in the political feud, experts said.

"The humanitarian situation is clearly not a priority at the moment," said Pooven Moodley of Oxfam.

Once a regional breadbasket, the United Nations estimates that more than five million people -- nearly half the population -- need emergency food aid this year.

About 80 percent of the population is unemployed and living under the poverty line of two US dollars per day.

And analysts say they doubt that South Africa's new President Kgalema Motlanthe will move to exert more pressure on Mugabe than Mbeki did when he was in office.

"I don't think South Africa is going to change its position," Moeletsi Mbeki said. (AFP)