Opposition candidate Michael Sata held a slim lead over acting President Rupia Banda in Zambia's presidential vote early on Saturday as election officials continued to count ballots.

Sata had 40 percent of the vote compared to 38 percent for Banda in 102 of 150 constituencies, giving him a lead of just 27 019 ballots, said Electoral Commission of Zambia Chairperson Florence Mumba.

The Patriotic Front (PF) leader, who has accused Banda's ruling Multiparty Movement for Democracy (MMD) of seeking to rig the vote, had a wider earlier in the tally but his lead narrowed as the counting progressed.

"We are very confident to the extent of being sure," the MMD's Akashambatwa Mbikusita-Lewanika told AFP after the latest tally.

"The electoral results have followed an established pattern and we are privy to the results at the polling stations so there are no surprises," he said.

Final results were expected later on Saturday.

Allegations of vote rigging

Tense allegations of vote rigging resurfaced late on Friday with the PF accusing the ruling party of election fraud and of "deliberately provoking" it and Zambian citizens before the final vote was verified.

This was after an MMD official predicted on national television that Banda would win by some 60 000 votes, which PF spokesperson Given Lubinda claimed was meant to "preempt their planned actions to manipulate these election results".

But ruling party spokesperson Tetama Shimba dismissed the claims as petty, saying that the prediction was based on polling station totals which had been posted at each vote station and were in the hands of all political parties.

Although observers and election officials said voting went smoothly on Thursday, police and soldiers remained on alert for possible violence after the hotly contested race was announced.

Protests were likely whichever party won, said Lee Habasonda, executive director of the Southern African Centre for the Constructive Resolution of Disputes.

"Unrest is very likely"

"Unrest is very likely because both the two leading contenders believe they cannot lose this election," he told AFP.

Sata has repeatedly accused authorities of planning to rig the election, and on Thursday he again warned that he would not accept a loss to the MMD, accusing police of conspiring with electoral officials to rig the vote.

The election commission has consistently denied any wrongdoing, and its spokesman Cris Akufuna said that voting proceeded without serious incident.

Observers from the African Union also said the election had gone smoothly.

The poll was called after president Levy Mwanawasa died in August following a stroke. The winner will serve until the end of Mwanawasa's term in 2011.

Fiery rhetoric

Sata (71) nicknamed "King Cobra" for his fiery rhetoric, promised better jobs and housing in a campaign against poverty.

He has also vowed to force foreign companies to hand 25 percent stakes to local investors, and is an open admirer of neighbouring Zimbabwe's controversial President Robert Mugabe.

Although he has little formal education, he is a shrewd political operator who rose to top level government before breaking off to form his own party.

Banda (71) is a Western-educated former diplomat who campaigned on promises to maintain Mwanawasa's economic policies, which led Zambia through years of sustained growth.

He has made his own populist pitch to rural farmers, slashing the price of fertiliser by 75 percent in the week before the election.

Although Mwanawasa has reined in inflation and built up impressive foreign reserves, Zambia remains one of the world's poorest countries with more than 60 percent of the population living on less than two dollars a day.

AFP