South Africa's new leader, Kgalema Motlanthe on Thursday backed former president Thabo Mbeki as the mediator in Zimbabwe, saying he would revive a stalled key power-sharing deal he brokered last month.

"Our government has full confidence in Mr Mbeki's ability to build on the historic successes already made in the power-sharing negotiations under his mediation," President Kgalema Motlanthe said in a statement.

"Therefore, we will further fully support him as the facilitator," he added.

Motlanthe took office last week after Mbeki was forced to resign due to a power struggle in South Africa's ruling party after he got Zimbabwe's political rivals to sign a deal for a unity government to end a ruinous political crisis.

Mbeki's resignation raised concerns about the future of the deal, which bogged down this week after President Robert Mugabe and opposition leader Morgan Tsvangirai failed to agree on how to divide key ministries.

Motlanthe said he had informed the Southern African Development Community (Sadc) of his government's support for Mbeki's continued rule as the regional bloc's mandated facilitator.

Mbeki's efforts had proven his "dispassionate vision for a lasting political solution to the challenges facing Zimbabwe", he said.

The agreement signed on 15 September had been hailed as a breakthrough in Zimbabwe's political crisis, sparked after Mugabe lost a first round of elections in March.

Negotiations appeared at a stalemate, with Tsvangirai's Movement for Democratic Change (MDC) claiming that Mugabe wants to retain key posts ? believed to be the defence, home affairs, state security and finance ministries.

After Mugabe and Tsvangirai failed to resolve their differences during a meeting on Tuesday, the MDC called on Mbeki and the regional bloc Sadc to resume their mediation to break the logjam.

But the chief negotiator for Mugabe's ruling Zanu-PF party denied any deadlock, saying no outside mediation was needed.