FACTBOX: What next in Zimbabwe's elections?

(Reuters) - Below are answers to some key questions as counting continues after Zimbabwe's elections, in which President Robert Mugabe faced an unprecedented challenge to his 28-year rule.

WHAT DO THE RESULTS SHOW?

Not much so far. Only a few parliamentary results have been issued by the electoral commission, under pressure to explain a delay that has fuelled accusations of rigging.

First parliamentary constituency results were evenly split between Mugabe's ZANU-PF and the opposition Movement for Democratic Change (MDC). However the opposition says its own unofficial count shows it with 60 percent of the presidential vote and 96 out of 128 known seats. There are 210 parliamentary constituencies.

Analysts say early counting tends to come from the opposition's urban strongholds whereas later results will include rural areas that are Mugabe's traditional base.

WHY ARE DELAYS SIGNIFICANT?

In past elections, results emerged quickly. The electoral commission says it is more complicated now because presidential, parliamentary and local elections were held together for the first time.

Further delays would stoke opposition suspicions of rigging to ensure the continued rule of Mugabe, blamed by opponents for an economic crisis that has ruined Zimbabwe. He blames Western sanctions. Analysts say delays increase the danger of rumors and violence.

"In a polluted environment, as you find in Zimbabwe, of polarization and suspicions that there could be attempts to rig the elections, minor issues such as the delay in the results fuel suspicion that what many people had in mind is indeed being confirmed," said Siphamandla Zondi of South Africa's Institute for Global Dialogue think-tank.

HOW DID VOTING GO?

There were no major reports of violence in Saturday's vote but the opposition and one African observer group reported irregularities -- including rolls with many non-existent or dead voters.

The main observer team from regional bloc SADC, long seen as being soft on Mugabe, said the vote looked free and fair but two members from South Africa's main opposition party dissented and refused to sign a preliminary report.

Most international observers were banned.

WHO WILL WIN?

Morgan Tsvangirai's opposition MDC says it won based on local vote counts pinned up outside polling stations. The government has warned such premature declarations could amount to "a coup".

Many analysts expect the result to be manipulated and said Mugabe would declare victory even if he lost. Security service chiefs have said they would not accept an opposition win. Tsvangirai and some international observers said Mugabe lost the last presidential election in 2002 but he stayed in power.

If no candidate gets over half the votes in the first round of the presidential election, there would be a run-off.

WHAT IF MUGABE WINS?

If Mugabe wins the presidential poll outright, this is certain to be rejected by the opposition MDC and some of its supporters could take to the streets. However a Kenyan scenario of prolonged protests and bloodshed seems unlikely.

Riot police have already been deployed to suppress demonstrations and they would be expected to subside quickly.

Some analysts believe Mugabe would be forced to carry out some reforms, even if he stayed in power, to try to ease the dire economic crisis and diplomatic isolation, but he showed no sign of readiness to do so during his campaign.

WHAT IF THERE IS A RUN-OFF?

A second round could unite the opposition. The campaign of Simba Makoni, whose split from the ruling ZANU-PF party showed up its internal divisions, has already said he would swing his support behind Tsvangirai. Makoni appears to have done badly in the vote, falling into a distant third place.

If there is a run-off, Mugabe would be expected to deploy ZANU-PF militants and independence war veterans to ensure victory, raising the prospect of violent clashes with defiant MDC supporters in the three-week hiatus between votes.

A run-off is likely to end with Mugabe being declared victor, leaving political tension and no prospect of saving the economy. Western powers would likely tighten sanctions and Mugabe's power within the party may be weakened. He would be expected to purge suspected Makoni allies.

WHAT IF TSVANGIRAI WINS?

If Tsvangirai wins, ZANU-PF militants and security forces are likely to reject his victory, leading to a violent crackdown against the MDC. Tsvangirai has said he would form a national unity government, bringing in moderate elements of ZANU-PF.

(Reporting by Cris Chinaka, Barry Moody and Phumza Macanda; Editing by Matthew Tostevin)