Opposition leader Morgan Tsvangirai has quit the Zimbabwe's bitterly fought run-off election, saying the vote cannot be free and fair.
Mr Tsvangirai cited violence as the major reason for withdrawing.
Earlier, armed supporters of Zimbabwe's ruling ZANU-PF attacked people attending a MDC rally.
'We in the MDC cannot ask them to cast their vote on the 27th when that vote would cost them their lives,' Mr Tsvangirai said.
Mr Tsvangirai also urged the United Nations and African Union to intervene to prevent a 'genocide'.
South Africa has urged Zimbabwe's opposition to continue with talks to find a solution to the political problems.
EU foreign policy chief Javier Solana said that the Zimbabwe opposition leader's decision to quit a presidential run-off was 'understandable' given the authorities' violence.
'In these conditions, the elections have become a travesty of democracy. They are certainly not worthy of the African continent of today,' he added.
The US has called for the Zimbabwe government and 'its thugs' to stop violence.
Robert Mugabe cannot be the legitimate leader of the country now that the opposition has pulled out of an election run-off, British Foreign Secretary David Miliband warned.
The MDC will formally withdraw party leader Morgan Tsvangirai from the June 27 presidential run-off vote, a MDC spokesman confimed.
'The unfortunate thing is that they (Zimbabwe Electoral Commission) want to jump the gun. They will get the letter. The resolution was only made today. We will give them their letter.' MDC spokesman Nelson Chamisa said.
Earlier the electoral commission said the presidential run-off election will go ahead because opposition leader Morgan Tsvangirai has not formally announced his withdrawal.
ZANU-PF said Mr Tsvangirai quit the run-off 'to
avoid a humiliating defeat' it added that he had no other option.
Yesterday, Mr Tsvangirai said that no one had the right to cancel an election.
South African President Thabo Mbeki had reportedly been seeking to have the run-off cancelled in favour of talks on forming a national unity government.
