The Zimbabwean opposition leader today called on the South African president, Thabo Mbeki, to stand down as a mediator and make way for a new initiative.

Morgan Tsvangirai has been pressing Mbeki to drop his approach of "quiet diplomacy" and put pressure on Robert Mugabe to give up power following his apparent loss in the March 29 presidential elections.

South Africa today hardened its position towards Mugabe when its government spokesman called for the prompt release of the election results.

"The most important thing is that the results need to be verified and released as soon as possible," Themba Maseko said.

This, however, was too little, too late for Tsvangirai, the leader of the Movement for Democratic Change (MDC), who claims to have won the presidential vote.

He told reporters he had asked the Zambian president, Levy Mwanawasa - who is also the chairman of the Southern African Development Community (SADC) - to launch a new initiative.

"President Mbeki needs to be relieved from his duty," Tsvangirai told a news conference in Johannesburg, adding that Mugabe had "unleashed an orgy of violence against the people" after the election.

Mbeki has resisted calling Zimbabwe's the post-election deadlock a crisis, and the US today criticised Africa for its lack of action on Zimbabwe.

"It is time for Africa to step up," the secretary of state, Condoleezza Rice, said. "Where is the concern from the African Union and from Zimbabwe's neighbours about what is going on in Zimbabwe?"

Nevertheless, diplomats in Zimbabwe said they had been encouraged by tougher statements from South Africa and particularly from Jacob Zuma, the head of the ruling African National Congress party.

"There is a feeling that South Africa's policy, which has been glacial, is finally changing, slowly, slowly," a diplomat said.

Despite a tougher line from the South African government, Pretoria agreed to let a shipment of Chinese weapons go through its territory to Zimbabwe.

A Chinese ship, the An Yue Jiang, docked in Durban harbour after receiving approval from port authorities late yesterday.

The Beeld newspaper said the vessel was carrying nearly 3m rounds of ammunition for small arms and AK-47 machine guns, about 3,500 mortars and mortar launchers and 1,500 rockets for grenade launchers.

South Africa said that as long as administrative papers were in order, it could not block shipments to its landlocked neighbour.

"We are not in a position to act unilaterally to prevent a trade deal between two countries," a government spokesman said, adding that there was no trade embargo against Zimbabwe.

China is one of Zimbabwe's main trade partners and allies.

The EU today called for the immediate publication of the election results. "Clearly, the publication of the results is needed, and it's needed now," a spokesman said.

"Further delays are unacceptable and would just be considered as stalling the democratic process."

Foreign ministers of the G8 group of eight industrialised countries, including the UK, made similar calls as they met in Tokyo.

They stressed that violence and intimidation must have no place in the process.

The Zimbabwean justice minister, Patrick Chinamasa, today accused Tsvangirai of treason.

"It is clear from the correspondence that Tsvangirai … is seeking regime change in Zimbabwe, and on the part of Tsvangirai this is treasonous," Chinamasa, quoted in state-controlled media, said.

"There is no doubting the consequences for acting in a treasonous manner."

Tsvangirai dismissed the claims as "outrageous".