Zimbabwe's main opposition leader says South Africa's president should step aside as the chief mediator in Zimbabwe's political crisis.

Morgan Tsvangirai's call at a news conference in South Africa Thursday follows comments from South African President Thabo Mbeki saying there is no crisis in Zimbabwe. Mbeki says confronting Mugabe could backfire.

Tsvangirai says Zambian President Levy Mwanawasa should take over the mediation Mbeki has led on behalf of regional leaders. Mwanawasa has taken a tough stance on Zimbabwean President Robert Mugabe.

Mugabe is accused of ruining his country's economy, undermining democracy and refusing to step down after an election Tsvangirai claims to have won.

Also on Thursday, Zimbabwe's government accused Tsvangirai of treason, saying that he and Britain are plotting to overthrow the president. Tsvangirai denounced the allegations as "outrageous."

President Robert Mugabe's government claimed in Zimbabwe's state-run newspaper that Tsvangirai is plotting an "illegal regime change" with the help of Britain, the former colonial power. The paper cited a letter from Britain's prime minister — which the opposition says is a forgery.

The accusation comes amid a government campaign of arrests, assaults and other intimidation designed to suppress political dissent following a March 29 vote that Mugabe is widely believed to have lost. Results from the presidential vote have not been released some three weeks after the ballot.

Independent tallies suggest Tsvangirai won, but not with enough votes to avoid a runoff. The electoral commission plans a re-count of presidential votes on Saturday, saying it is verifying ballots and investigating anomalies.

The opposition says Tsvangirai won outright, and accused Mugabe of engineering a delay to secure his 28-year grip on power.

On Thursday, Tsvangirai — in an exclusive interview with The Associated Press in Johannesburg, South Africa — dismissed the government's allegations as "outrageous."

He said his Movement for Democratic Change party was formed with a commitment to "democratic change" in Zimbabwe, not a forceful overthrow of the Mugabe regime.

Zimbabwe's government also said Thursday that it will pull the licenses of any transportation workers who heed opposition calls to strike for the release of the country's long-delayed presidential election results.

With Zimbabwe's economy already devastated by soaring inflation and 80 percent unemployment, the opposition has had difficulty getting the few Zimbabweans with jobs to stay home as part of a nationwide strike to press for the release of results.

But the state-run Herald newspaper said a number of public buses have stopped running in adherence to the strike.

The buses "have been deliberately withdrawing their services since Monday," Transport Minister Chris Mushohwe told the paper. Mushohwe said those workers are violating the terms of their licenses, which require them to provide public transportation.

"Once we withdraw the operating licenses, we would not be renewing any for those who are not operating," he said.