"The talks have reached a deadlock and cannot be moved forward. Apparently, the ZANU-PF negotiators were only mandated to negotiate around the vice presidency and nothing else," the MDC official told Reuters on condition of anonymity.

Senior negotiators from ZANU-PF and the MDC started the talks last Thursday, with the objective of finding a solution to the country's political and economic crisis, including the possibility of forming a unity government.

The negotiations followed preliminary talks that started on Tuesday after President Robert Mugabe and MDC leader Morgan Tsvangirai signed a deal on the framework for discussions to end the deadlock over Mugabe's re-election on June 27 in a poll boycotted by the opposition because of violence.

The MDC official said the opposition was unwilling to accept a deal for the post of vice president for Tsvangirai, who won the initial March 29 election but failed to get enough votes to avoid a run-off vote.

"The MDC is the largest party in parliament and all they could offer was the vice presidency? Obviously, the MDC's position is that that's not acceptable," the official said, adding that the ZANU-PF negotiators had reportedly left because of the stalemate.

Tsvangirai's spokesman George Sibotshiwe said the MDC chief had travelled to South Africa on Monday, but was on "private business" and would not meet with his negotiators.

But the MDC source said Tsvangirai would meet the negotiators on Tuesday, before proceeding to a meeting of the Southern Africa Development Community (SADC)'s organ on politics, defence and security in Angola on Wednesday.

Worried by a crisis that has flooded neighbouring states with millions of refugees, SADC and the African Union (AU) have pushed for a power-sharing deal in Zimbabwe.

The southern African grouping appointed South African President Thabo Mbeki mediator between ZANU-PF and the MDC last year.

Tsvangirai's MDC insists that he be the leader of any unity government because he won the first round of voting.

ZANU-PF, however, has said it will not accept any deal that fails to recognise Mugabe's re-election or seeks to reverse his land redistribution programme, which has seen the government seize thousands of white-owned farms beginning in 2000.

The parties also disagree over how long a national unity government should remain in power. Tsvangirai's MDC wants fresh elections held as soon as possible, while Mugabe, who has ruled since 1980, wants to carry on with his new five-year mandate.