Zimbabwean opposition leader Morgan Tsvangirai pulled out of the country's violence-wracked presidential runoff Sunday, declaring the election was no longer credible and the loss of life among his supporters was simply too high. The announcement cleared the way for President Robert Mugabe to continue his 28-year rule, despite mounting condemnation from even loyal African allies that the former independence hero has become a despot who has bankrupted his once thriving economy and embarrassed a continent that is embracing democracy. "We can't ask the people to cast their vote ... when that vote will cost their lives. We will no longer participate in this violent sham of an election," Tsvangirai said. He addressed a news conference in Zimbabwe's capital after thousands of militants loyal to Mugabe prevented opposition supporters from gathering for its main campaign rally - in a now-routine pattern of intimidation. As night fell, militia groups roamed the capital. Normally busy Sunday traders packed up early and tension was high. Hotels sent their workers home early out of fear for the safety. Tsvangirai called on the United Nations, the European Union and the Southern African regional bloc to intervene. In an unusually strong response, UN Secretary-General Ban Ki-moon on Sunday blamed Zimbabwe's government for the breakdown in the election process and called for the run-offs to be postponed. Tsvangirai said he would put forward new proposals by Wednesday on how take the country forward. The opposition has repeatedly said it would welcome a government of "national healing" including ruling ZANU-PF party members but not Mugabe himself. Zimbabwean Information Minister Sikhanyiso Ndlovu said the runoff would go ahead in accordance with the constitution - and to prove Zimbabweans' support for their longtime leader. "The constitution does not say that if somebody drops out or decides to chicken out the runoff will not be held," Ndlovu said. "It is an election of the people of Zimbabwe against Britain and America," he said, returning to the government's theme of portraying Tsvangirai as a puppet of Western powers out to re-colonize Zimbabwe. The opposition, Britain and the United States reject such claims. Tsvangirai won the first round of the presidential election March 29, but according to official results did not gain an outright majority against 84-year-old Mugabe, who has held power since independence from Britain in 1980. That campaign was generally peaceful, but the runoff has been overshadowed by violence and intimidation, especially in rural areas. Independent human rights groups say 85 people have died and tens of thousands have been displaced from their homes, most of them opposition supporters. Ndlovu reiterated government claims that the opposition was to blame for the violence. Tsvangirai complained he was being treated like a "common criminal," with his attempts to tour the country stymied by police at roadblocks. The state-controlled media have banned opposition advertisements, claiming they "contain inappropriate language and information." The media cited one ad that claimed that Tsvangirai won the election, "which is not the case, hence the runoff." Tendai Biti, the opposition party's No. 2, was arrested within minutes of his return from South Africa last week and is being held on treason charges. Tsvangirai had hoped to address his main campaign rally for the runoff Sunday afternoon. But thousands of ruling party militants blockaded the show ground site and set up roadblocks at the main approach streets, ripped branches from trees and hurled stones at cars. Hundreds of militants, many with sticks and wearing ZANU-PF ruling party colors, marched past its headquarters chanting slogans. ZANU-PF trucks, warning lights flashing and crammed with passengers, circled the grounds. The opposition Movement for Democratic Change claimed the militants were beating opposition supporters who were trying to reach the venue and said at least two were seriously injured. It said the militants attacked journalists and forced African election monitors, who had been driving around the rally site, to flee. Election monitors could not immediately be reached for comment. Zimbabwe has barred Western observers and most journalists, but permitted African election monitors. Mugabe has shrugged off mounting international condemnation. But never before has he faced such criticism from other African leaders, who now openly say Mugabe is an embarrassment. Even one of Mugabe's staunchest allies, Angolan President Eduardo dos Santos, urged him to end "all acts of intimidation and violence," while current African Union chair Tanzania said it doubted the elections would be free and fair. The leaders of Rwanda and Kenya - which have both suffered deadly political violence - have been especially scathing. Zambian President Levy Mwanawasa said Sunday that the runoff must be postponed. Mwanawasa, who currently holds the rotating chair of the Southern African Development Community and has long been among Mugabe's most outspoken critics in the region, said Zimbabwe had failed to meet minimum election standards. He voiced particular frustration that he had been unable to reach South African President Thabo Mbeki, the region's designated mediator in the Zimbabwe crisis, and criticized Mbeki for not sharing information. Mbeki is increasingly isolated both abroad at at home for his appeasement of Mugabe and his refusal to flex South Africa's economic muscle against his neighbor. Mbeki's spokesman, Mukoni Ratshitanga, said Tsvangirai had called Mbeki earlier Sunday to inform him he was withdrawing. "Of course we would like to encourage the MDC to continue to play a role in the normalization of the political process in Zimbabwe. And we are encouraged that Mr. Tsvangirai says he is not closing the door completely on negotiations," said Ratshitanga. The European Union threatened Friday to step up sanctions against Mugabe's government, and the United States and Britain want a special UN Security Council meeting. British Foreign Secretary David Miliband voiced sympathy for the opposition decision. "It's evident Morgan Tsvangirai was left with no choice as he wanted to preserve the life and limb of his people," Miliband told the British Broadcasting Corp. "What's clear is that his (Mugabe's) rule has no legitimacy." In New York, UN Secretary-General Ban Ki-moon's office released a statement saying that he "deeply regrets that, despite the repeated appeals of the international community, the government of Zimbabwe has failed to put in place the conditions necessary for free and fair run-off elections." He said that the "circumstances that led to the withdrawal of opposition leader Morgan Tsvangirai today from the presidential elections represents a deeply distressing development that does not bode well for the future of democracy in Zimbabwe." "The campaign of violence and intimidation that has marred this election has done a great disservice to the people of the country and must end immediately," Ban said. The unusually blunt statement from the UN chief added that he "strongly supports" the Southern African Development Community's chairman's position that "conditions do not exist for a run-off election to be held at this time and that they should be postponed." At a rally in the western city of Bulawayo on Friday, Mugabe said the opposition was lying about the violence and that everywhere he visited was peaceful. His powerful police chief pinned the blame firmly on the opposition and said police would clamp down. Some analysts say a small inner circle of security chiefs has orchestrated the current violence as it is desperate to prevent an opposition victory and wants to keep Mugabe in power to retain its privileges and protect it from possible prosecution. Mugabe was lauded early in his rule for campaigning for racial reconciliation. But in recent years, he has been accused of ruining the economy and holding onto power through fraud and intimidation. The economic slide of what was once the region's breadbasket has been blamed on the collapse of the key agriculture sector after often-violent seizures of farmland from whites. Mugabe claimed he ordered the seizures, begun in 2002, to benefit poor blacks. But many of the farms instead went to his loyalists.