US President George W Bush has said the Zimbabwe run-off vote due this week has no credibility.
Friday's elections 'appear to be a sham,' Mr Bush said at the White House after meeting members of the UN Security Council.
He added that 'The Mugabe government is intimidating people on the ground in Zimbabwe'.
Southern African leaders earlier called for postponement of the election, saying conditions are not conducive to a fair poll.
The Southern African Development Community summit said holding the election under the current circumstances might undermine the credibility and legitimacy of its outcome.
Leaders of a security troika of the SADC comprising Tanzania, Angola and Swaziland spoke after talks on Zimbabwe near the Swazi capital Mbabane.
King Mswati of Swaziland and Tanzania's President Jakaya Kikwete were at the meeting, said a spokesman for Swaziland Prime Minister Absalom Themba Dlamini.
Meanwhile, the British Foreign Office has announced that the Zimbabwe president has been stripped of the honorary knighthood he was awarded in 1994.
A spokesman said the decision was 'a mark of revulsion at the abuse of human rights and abject disregard for the democratic process in Zimbabwe over which President Mugabe has presided.'
Thabo Mbeki is a mediator in the crisis between Mr Mugabe and the opposition, but his spokesman said that the South African leader was not going to Mbabane because he had not been invited.
'President Mbeki was not invited to because he is not a member of the troika, but the door is open for him to attend as a mediator to the Zimbabwe crisis,' the spokesman said.
A statement from the Tanzanian presidency had said yesterday that Mr Mbeki would attend the emergency meeting along with Kikwete and Zambian President and SADC Chairman Levi Mwanawasa.
The meeting in Swaziland's capital Mbabane was called by the SADC as international pressure mounts on Zimbabwe's President Robert Mugabe to resolve his country's political turmoil and economic meltdown.
Mr Mugabe's government yesterday vowed to go ahead with a presidential run-off election on Friday despite the withdrawal of opposition candidate Morgan Tsvangirai, citing political violence against his supporters.
South Africa's governing ANC party accused his government of riding roughshod over democracy. The US Assistant Secretary of State for African Affairs, Jendayi Frazer, said her government would not recognise the outcome of Friday's vote.
Mr Tsvangirai, who is now in the Dutch embassy in Harare, quit the race in an official letter to the electoral commission yesterday.
The opposition pull-out has laid out a possible victory by default for veteran leader Mr Mugabe, in power since 1980.
Friday's vote was meant to be a run-off between Mr Mugabe and Mr Tsvangirai. The opposition leader won a first round in March but official figures did not give him an outright victory.
Mr Tsvangirai's Movement for Democratic Change won a parallel parliamentary election in March, sending Mr Mugabe's ZANU-PF party to its first defeat since independence from Britain in 1980.
The SADC is facing a storm of criticism for its failure to ensure transparent and violence-free elections in Zimbabwe.
Several Western nations, including Britain and the US, have urged the world to isolate Mr Mugabe and declare his presidency illegitimate if there is not a free and fair ballot.
Tsvangirai urges UN to isolate Mugabe
Earlier, Mr Tsvangirai urged the UN to isolate President Mugabe and said a peacekeeping force was needed in Zimbabwe.
He said Zimbabwe would 'break' if the world did not come to its aid.
'We ask for the UN to go further than its recent resolution, condemning the violence in Zimbabwe, to encompass an active isolation of the dictator Mugabe,' Mr Tsvangirai wrote in an article in the Guardian newspaper.
'For this we need a force to protect the people. We do not want armed conflict, but the people of Zimbabwe need the words of indignation from global leaders to be backed by the moral rectitude of military force,' said Mr Tsvangirai.
'Such a force would be in the role of peacekeepers, not trouble-makers. They would separate the people from their oppressors and cast the protective shield around the democratic process for which Zimbabwe yearns.'
