HARARE, ZIMBABWE -- The Zimbabwean opposition said today that no one from the party would meet with visiting South African President Thabo Mbeki, who it says should be replaced as mediator in the country's political crisis.

President Robert Mugabe met Mbeki at the airport today as the South African leader arrived for his third visit as mediator on behalf of the Southern African Development Community.

The two men, wearing flower garlands, laughed as they walked hand-in-hand from the aircraft. They did not speak with reporters, but later posed for photographs in Mugabe's residence, State House, where they held a meeting lasting nearly four hours.

Mbeki was expected to leave Zimbabwe later today.

But opposition leader Morgan Tsvangirai will not be sitting down with Mbeki, whom he sees as biased toward Mugabe, opposition spokesman George Sibotshiwe said.

Tsvangirai "has no confidence in Mbeki," and has called for him to step aside and allow Zambian President Levy Mwanawasa to take over mediation, Sibotshiwe said.

Mwanawasa has been more critical of Mugabe, while Mbeki -- believing Mugabe would not respond to confrontation -- has stuck to "quiet diplomacy" on Zimbabwe.

Mugabe and Tsvangirai have been in a tense political standoff. The opposition leader insists he won March 29 presidential elections outright.

The electoral commission said last week that Tsvangirai had won the most votes but failed to win the simple majority required for a first-round victory, and so would have to face Mugabe again in a runoff.

Mugabe has been accused of orchestrating violence against the opposition since the first round, raising questions about whether a runoff would be free or fair.

Tsvangirai's party, the Movement for Democratic Change, is expected to make an announcement Saturday in South Africa on whether it will take part in a runoff.

No date has been set for the vote, although Mugabe has already begun campaigning.

Meanwhile, opposition party supporters are increasingly under attack.

The Zimbabwe Association of Doctors for Human Rights said 22 people had died and 900 were tortured in postelection violence.

But "violence is now on such a scale that it is impossible to properly document all cases," the association said in a statement today, citing a "dramatic increase" in violence since the start of May.

In the last 24 hours, Harare hospitals and clinics have treated 30 people for broken limbs, the association said. Those admitted to hospitals with injuries included elderly men, breast-feeding women and a 3-year-old boy struck in the eye by a rock, it said.

"The level of brutality and callousness exhibited by the perpetrators is unprecedented," the statement said.

The doctors also raised concerns about the intimidation of health workers and a shortage of medical supplies.

Meanwhile, the deputy director of army public relations, Maj. Alois Makotore, denied accusations that soldiers had harassed or assaulted people, the state-owned Herald newspaper reported today.

The newspaper also accused opposition supporters of burning the homes of ruling party supporters. Government and party officials have denied they were responsible for the violence and instead blamed the opposition.

Carolyn Norris from Human Rights Watch, speaking today by telephone from London, said opposition supporters had occasionally retaliated, but that violence on the opposition's part was "tiny in proportion to absolute campaign of violence and intimidation by the ruling party." She said there was no evidence of the opposition "organizing a revenge campaign."