Zambia’s main opposition leader filed papers in the constitutional court on Friday challenging the re-election of President Edgar Lungu in last week's vote.
Hakainde Hichilema, who heads the United Party for National Development (UPND), wants the outcome of the fiercely fought elections which gave Lungu a narrow win, to be set aside.
He claims the victor did not attain the required threshold for one to be declared winner.
In the filed papers, Hichilema said Lungu "did not receive more than 50 percent of the total votes cast" as required by the law.
According to the poll results released by the country's electoral commission on Monday, Lungu won the elections by 100,000 votes, or 50.35 percent of the vote against 47.63 percent for Hichilema, just enough to avoid a run-off.
"We are asking for the nullification of the election," Gilbert Phiri, a lawyer for Hichilema's UPND, told reporters.
The 54-year-old businessman who was making his fifth bid for the presidency has rejected the August 11 poll as rigged.
"The voter register was not credible and (its) non-availability before the election compromises the transparence of the electoral process," read the petition.
He also says in the petition that the number of ballots cast in favour of Lungu was inflated by fake, pre-marked ballots, and asked that the court nullify Lungu's victory.
The court has 14 days to hear the petition, and should make its ruling within a month.
The petition means the inauguration of the president which had been set for Tuesday, will have to be delayed until the court's decision.
The speaker of parliament should take over the presidency until the court delivers its ruling, according lawyer Phiri.
Before his re-election, Lungu had been in office for just 19 months after he took power in a snap election following the death in office of president Michael Sata, again beating Hichilema by a tiny margin.
Zambia, which gained independence from Britain in 1964, has a long history of peaceful power transitions.
About 60 percent of the population of Africa's second biggest copper producing nation live below the poverty line, according to the World Bank.