The Patriotic Front’s formal request to Zambia’s electoral commission came several hours after PF leader Michael Sata accused officials of rigging the vote to prevent him from ruling the mineral-rich southern African nation.
Sata, a populist with strong support among workers and the poor, has been alleging electoral fraud since shortly after the polls closed on Thursday. He made the same charge when he lost the 2006 presidential election to late President Levy Mwanawasa.
Mwanawasa died in August after suffering a stroke, triggering the election. Zambia is Africa’s largest copper producer and is one of the continent’s most stable countries, politically and economically.
Earlier on Saturday, Sata stormed into the Lusaka conference hall where results were being announced and said: "I have evidence that results are being inflated … They cheated me in 2006 and they want to do the same."
Preliminary results released on Saturday afternoon showed Sata with 666,194 votes versus 652,354 votes for Banda. The count was based on results from 137 of 150 constituencies. Some 3.9 million Zambians were registered to vote in the poll.
With the bulk of ballots in Lusaka, a Sata stronghold, counted, it is possible Banda could pull ahead when more votes from pro-government rural areas are factored into the tally. The next set of results is expected at around 1600 GMT.
Sata, popularly known as "King Cobra" for his political manoeuvring, renewed his fraud accusations after election officials said the counting was proceeding slowly.
"We are slow because we have to verify all the results," said Chris Akufuna, a spokeswoman for the electoral commission.
Independent election monitors have noted some irregularities in the poll but have stopped short of condemning the vote.
It is unclear what Sata and his supporters will do if Banda is declared the winner. The PF leader has suggested several times since Thursday that he will not accept any result that allows Banda to remain in office.
Zambia’s army has been put on alert to prevent unrest and its army chief has said he will not tolerate violence.
The winner faces the formidable task of matching Mwanawasa’s strong record of fiscal discipline, praised by Western donors and investors, and cracking down on corruption, two rare successes in Africa.
The vote also is seen as a test of Zambia’s commitment to multi-party democracy, restored in 1990 after 18 years of one-party rule under Kenneth Kaunda, but neither Banda nor Sata is expected to reshape the political landscape dramatically.
Banda, who leads the Movement for Multi-Party Democracy, is hoping to benefit from Zambia’s relative prosperity as well as Mwanawasa’s enduring popularity. He has pledged to maintain the government’s pro-business policies if elected.
The economy has grown at an average of 5 percent per year since 2002, boosted by the sharp rise in world commodity prices.
Inflation has fallen from more than 200 percent in 1991 to about 14 percent.
But 65 percent of Zambia’s 12 million people live on less than $1 a day and more than one million are HIV positive.