Morgan Tsvangirai, the Zimbabwean opposition leader, finally lost his patience with Thabo Mbeki today over the South African President's refusal to recognise the post-election deadlock as a crisis.

The Movement for Democratic Change (MDC) seized control of parliament from Robert Mugabe's Zanu (PF), according to official results from the March 29 election and Mr Tsvangirai also claims to have won the presidency from Mr Mugabe, but official results from the presidential contest have still not been released.

At a press conference in Johannesburg, Mr Tsvangirai called for Mr Mbeki to hand over the role of mediator to his Zambian counterpart. He added: "We want to thank President Mbeki for all of his efforts but President Mbeki needs to be relieved of his duties [as mediator]."

The call appeared to reflect a general hardening of positions: only a few hours earlier, Zanu (PF) officials accused Mr Tsvangirai of treason and of working with Britain to oust Mr Mugabe.

Patrick Chinamasa, the Justice Minister, said he had seen correspondence showing that the MDC had asked Gordon Brown to depose Mr Mugabe and install him as president.

"It is clear from the correspondence that Tsvangirai along with Brown are seeking an illegal regime change in Zimbabwe and on the part of Tsvangirai this is treasonous," Mr Chinamasa said. "There are no doubting consequences for acting in treasonous manner."

Ironically, Mr Tsvangirai's criticism of Mr Mbeki came as the South African Government appeared to toughen its stance on Zimbabwe with a call for Mr Mugabe to publish the election results.

"The situation is dire," Themba Maseko, a government spokesman, said after a Cabinet meeting in Cape Town. "When elections are held and results are not released two weeks after, it is obviously of great concern."

Mr Mbeki, leader of the region's most powerful state, has come under fire for being too lenient towards his Zimbabwean counterpart during the post-election deadlock and confusion.

The Zimbabwe Electoral Commission says the elections are being held up by a recount planned for this weekend, which could see the official parliamentary results amended and a second round run-off vote declared for the presidency.

Mr Mbeki chaired a top-level meeting of the UN Security Council in New York yesterday at which Mr Brown declared that Mr Mugabe should not be allowed to "steal the election" – but Nelson Mandela's successor did not even mention Zimbabwe.

Mr Tsvangirai said that he had asked President Mwanawasa of Zambia, the current chairman of the Southern African Development Community (SADC), to begin a new mediation effort.

"I made a specific request to President Mwanawasa to say he needs to lead a new initiative, an initiative that will expand beyond that of Mr Mbeki."

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