Southern African leaders will hold an emergency meeting on Wednesday to discuss Zimbabwe's crisis, but the region's designated mediator, South African President Thabo Mbeki, will not attend, officials said.

The meeting in Swaziland's capital Mbabane was called by the 14-nation regional body, the Southern African Development Community (SADC), as international pressure mounted on President Robert Mugabe to call off a presidential election on Friday.

The leaders of a SADC security troika of Tanzania, Angola and Swaziland would attend the meeting, the Tanzanian government said in a statement.

It said Mbeki had been invited, together with Zambian leader Levy Mwanawasa, but Mbeki's spokesman said he would not go.

The South African president has been negotiating between Mugabe and Zimbabwe's opposition since last year but has been widely criticised for being ineffective and too soft on Mugabe.

Opposition leader Morgan Tsvangirai, who has withdrawn from the election, urged the United Nations to isolate Mugabe and called for a peacekeeping force in Zimbabwe.

Mugabe has refused to call off the vote, shrugging off mounting international pressure including Monday's unprecedented U.N. Security Council condemnation of violence. It said a free and fair run-off election on Friday was impossible.

The Tanzanian statement said: "The meeting will discuss how the SADC and its troika organ on politics, defence and security can help Zimbabwe to get out of its current state of conflict."

Mbeki spokesman Mukoni Ratshitanga told Reuters: "We are not going to Swaziland. We have had no invitation to go to any meeting, especially Swaziland." He said Mbeki also had no plans to visit Zimbabwe this week.

The Zimbabwe government also said it had not been invited.

"We do not even know there is a SADC summit on Zimbabwe in Mbabane," Justice Minister Patrick Chinamasa said.

INTERNATIONAL CONDEMNATION

There has been wide international condemnation of the violence but SADC is seen as the only body that can influence events in Zimbabwe. Several of its members have been flooded by millions of refugees fleeing the economic collapse of the once prosperous country.

Tsvangirai, who has taken refuge in the Dutch embassy in Harare since Sunday, said Zimbabwe would "break" if the world did not come to its aid.

"We ask for the U.N. to go further than its recent resolution, condemning the violence in Zimbabwe, to encompass an active isolation of the dictator Mugabe," he wrote in the Guardian.

"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 Tsvangirai.

"Such a force would be in the role of peacekeepers, not troublemakers. They would separate the people from their oppressors and cast the protective shield around the democratic process for which Zimbabwe yearns."

Pressure has increased on Mugabe from both inside and outside Africa over Zimbabwe's political and economic crisis, blamed by the West and the opposition on the 84-year-old president, who has held power for 28 years.

The United States urged SADC to declare both the election and Mugabe's government illegitimate.

Friday's vote was meant to be a run-off between Mugabe and Tsvangirai. The opposition leader won a first round in March but did not get the absolute majority needed to avoid a run-off.

Both Senegalese President Abdoulaye Wade and the leader of South Africa's ruling African National Congress said Friday's election must be postponed after Tsvangirai's withdrawal.

ANC leader Jacob Zuma, who rivals Mbeki as South Africa's most powerful man, called for urgent intervention by the United Nations and SADC, saying the situation in Zimbabwe was out of control.

Mugabe remained defiant, telling a rally in western Zimbabwe on Tuesday:

"The West can scream all it wants. Elections will go on. Those who want to recognise our legitimacy can do so, those who don't want, should not."