Both sides have been under heavy African and world pressure to enter negotiations since Mugabe's re-election in a June 27 poll scarred by campaign violence.

Diplomatic sources in Pretoria said the talks had begun in South Africa without specifying the location.

The Movement for Democratic Change (MDC) opposition, which boycotted the election because of violence that it said killed 103 of its supporters, had until now refused to enter talks.

It said negotiations could not resume until the violence ended and Mugabe accepted the result of the first round of the election in March, won by MDC leader Morgan Tsvangirai.

An MDC source in Harare said the talks were preliminary and would discuss ending the violence.

"Our team is in South Africa, where they will have preliminary talks with ZANU-PF, starting today. It means something is happening. So these are not the actual talks, but preliminary discussions on what the talks will focus on," the source said.

"This is where we are going to talk about issues of violence and it is from these discussions that the MDC will decide whether to engage in full negotiations if our conditions for an end to political violence are met. We will also have to agree on the agenda for the talks."

The new talks are being mediated by South Africa, designated as lead negotiator by the Southern African Development Community (SADC). The diplomatic sources said a breakaway faction of the MDC, led by Arthur Mutambara, was also taking part.

Zimbabwe's High Court on Wednesday relaxed bail conditions on MDC Secretary-General Tendai Biti and gave him back his passport, responding to a petition by his lawyers who said he should be allowed to travel for talks in South Africa.

Biti faces charges of treason.

CRISIS

The June 27 election and its condemned outcome have worsened the crisis in Zimbabwe, whose economy has collapsed, sending millions of refugees into neighbouring states including South Africa and increasing pressure for a solution.

The once prosperous nation is crippled by the world's worst inflation rate, estimated to be at least 2 million percent.

Mugabe, 84, has been in power since independence from Britain in 1980.

The African Union, at a summit last month, called for talks leading to a national unity government.

Many AU members oppose sanctions but Liberian President Ellen Johnson-Sirleaf on Thursday came out in favour.

She told reporters in Johannesburg that the sanctions move was intended to send a message to African leaders that they should do something about Zimbabwe.

"Sanctions don't always work, as you know. But I think the fact that it does send a strong message about the disagreement against those things that are really causing a country and its people to suffer makes it appropriate for those actions."

Anglophone West African countries like Sierra Leone, Liberia and the continent's most populous nation, Nigeria, have been among Mugabe's strongest critics, together with his neighbours in Botswana and Zambia.

Tsvangirai defeated Mugabe in a March 29 first round presidential poll but fell short of the absolute majority required to avoid a run-off.

Mugabe blames the opposition for the bloodshed.

Western nations led by former colonial ruler Britain and the United States are pushing the U.N. Security Council this week to impose sanctions on Mugabe's inner circle, as well as an arms embargo on Zimbabwe.

A G8 summit in Japan this week supported sanctions.

South Africa, backed in the past by veto wielding council members Russia and China, opposes sanctions.

Word of the new talks in South Africa may weaken support for the Western-sponsored resolution.

South African President Thabo Mbeki has mediated unsuccessfully in the Zimbabwean crisis for more than a year, drawing increasing criticism. The MDC say he favours Mugabe and has called for expanded mediation from the AU and the United Nations.

Johnson-Sirleaf also called for another mediator and suggested a high-profile figure.

Some African leaders support a power-sharing solution in Zimbabwe like the one mediated by former U.N. Secretary-General Kofi Annan to end Kenya's bloody post-election crisis this year.