JOHANNESBURG, August 3, 2008 (AFP) - Zimbabwe's rival parties were to resume power-sharing talks on Sunday, a day ahead of the expiry of a deadline to conclude discussions to end a ruinous and dragging political crisis.

After a nearly week-long break following suggestions the talks were deadlocked, negotiators were due to meet in South Africa to resolve the crisis, which intensified after President Robert Mugabe's controversial re-election.

'They will start in the afternoon,' said Mukoni Ratshitanga, spokesman for South African President Thabo Mbeki, who has been mediating the discussions that have been held in a secret location.

A spokesman for the opposition Movement for Democratic Change (MDC), Tapiwa Mashakada, confirmed the party's negotiators had returned to Pretoria for Sunday's meeting.

Officials from the ruling ZANU-PF party could not be reached, but Zimbabwe's state-run Sunday Mail quoted an anonymous source saying representatives for both sides had arrived in the South African capital.

The meeting comes after a bomb exploded at Harare's main police station Saturday night, shattering windows and damaging 13 offices and a kitchen, but causing no injuries, police said.

The talks broke up on Tuesday as negotiators flew home to consult with their leaders amid suggestions by the MDC that discussions on power sharing between Mugabe and rival Morgan Tsvangirai were deadlocked.

Mbeki flew to Harare for talks with Mugabe after the adjournment and also met Tsvangirai in Pretoria.

The South African leader, who has faced heavy criticism in the past for treating Mugabe with kid gloves, said in Harare that the talks were 'progressing'.

There have since been signs that the two-week deadline set out in a July 21 deal laying the framework for discussions would not be met, with Tsvangirai saying last week that the timeframe was 'not inflexible'.

Ratshitanga said Sunday the deadline should apply only to the number of days spent negotiating.

'That two weeks has got to be looked at from the point of view that they did take a four- or five-day break to go and consult,' he said.

Tsvangirai finished ahead of Mugabe in the March first round of the presidential election, but boycotted the run-off, citing rising violence against his supporters that left dozens dead and thousands injured.

He announced his withdrawal five days ahead of the June 27 election, and Mugabe pushed ahead with the vote despite regional and international calls to postpone it, handing himself a sixth term as president.

The two arch-rivals recently held a rare face-to-face meeting.

Tsvangirai believes his first-round total gives him the right to the lion's share of power, but sources in his party said recently Mugabe's negotiators had so far only offered him one of several vice presidential posts.

The ruling party has insisted Mugabe must be recognised as president as part of any deal, since he won the June 27 vote.

In a television interview last week, Tsvangirai declined to comment on his or Mugabe's respective roles in any interim government, but said the 84-year-old president should be allowed an 'honourable exit' from power.

He also stressed that a transitional government should last no more than two years.

Mugabe last week expressed his 'total commitment' to the negotiations, which also include an MDC splinter faction led by Arthur Mutambara, insisting they were 'going well'.

'We are still negotiating, we want to succeed..,' Mugabe said.

'We would like to see the speedy conclusion of the talks ... and successful outcome so that we can focus in the future our attention around our economy.'

The former British colony's economy has been in meltdown since Mugabe began a chaotic land reform programme at the turn of the decade, and inflation now stands at a staggering 2.2 million percent according to an official estimate.