Zimbabwean officials have said a run-off presidential election will go ahead, despite the withdrawal of opposition candidate Morgan Tsvangirai. Justice Minister Patrick Chinamasa said Mr Tsvangirai's announcement was a ruse - he had not sent a formal notice yet. Mr Tsvangirai said he would pull out to protect people from violence by ruling party Zanu-PF militias his party blames for killing 86 opposition supporters. The move has sparked international criticism of Zimbabwe's government. But President Robert Mugabe has blamed the opposition party, the Movement for Democratic Change, for the recent violence. The leader of neighbouring Zambia, Levy Mwanawasa - who is head of the regional Southern Africa Development Community (Sadc) - said a vote held in current conditions would be an "embarrassment" to the region. Meanwhile, African Union Commission chairman Jean Ping said he was worried about the situation. "This development and the increasing acts of violence in the run-up to the second round of the presidential election are a matter of grave concern to the Commission of the AU," he said. The US and UK have said they are prepared to bring Zimbabwe before the UN Security Council over the election violence. But South African President Thabo Mbeki, who is mediating in the crisis, called for further dialogue. "From our point of view it is still necessary that the political leadership of Zimbabwe should get together and find a solution to the challenges that face Zimbabwe," he said. 'Humiliation fear' Mr Chinamasa said Zanu-PF was not treating Mr Tsvangirai's "threats" to withdraw seriously. "This is the 11th time that Tsvangirai has threatened to withdraw from the presidential run-off and on each occasion I have challenged him to put it in writing as required by the law," he said. Mr Tsvangirai's announcement of withdrawal was to avoid "humiliation", he added. "Tsvangirai went into the election thinking that it was a sprint and was not prepared for a marathon and wants to avoid defeat," he said. "He spent his time globe-trotting and gallivanting in Europe and left MDC-T supporters without leadership." There has been no response from Mr Mugabe himself to Mr Tsvangirai's announcement. On Sunday, Mr Tsvangirai said that there was no point running when elections would not be free and fair and "the outcome is determined by... Mugabe himself". He said that while the decision had been a difficult one it was necessary to protect the people of Zimbabwe. The opposition's decision was announced after its supporters, heading to a rally in the capital Harare, came under attack. The BBC's Peter Biles says Mr Tsvangirai did not want to expose his supporters to any more violence. He will now be hoping that the Sadc will refuse to confer legitimacy on the process, he says. The BBC's correspondent adds that the country's economic crisis - with unofficial figures putting inflation at 2m% - could drive Zimbabwe's government to negotiate for a political solution. The MDC won the parliamentary vote in March, and claims to have won the first round of the presidential contest outright. In the official results, Mr Tsvangirai led but failed to gain enough votes to avoid a run-off. Source: BBC