Zambian President Edgar Lungu said on Tuesday his inauguration would be delayed until a court rules on a challenge from his main election rival who said the vote was rigged.
Results on Monday showed Lungu narrowly won re-election in Africa's second-largest copper producer which is suffering an economic slump due to depressed commodity prices.
But his rival, opposition leader Hakainde Hichilema, said he would challenge the result, alleging fraud during the vote counting process after Thursday's election.
Police said they arrested about 150 protesters in opposition strongholds in the southern African country, while one ruling party supporter was detained on Monday after torching a police vehicle during celebrations.
A rule introduced in January says the winner of a presidential election cannot be sworn in if the vote is contested in a court, which has two weeks to decide on such a petition.
Wearing a white T-shirt with the victory symbol and the words 'I love peace' on it, the president told his supporters at a victory rally in the capital Lusaka: "We will have to wait before I am sworn in because I am told some people have gone to court. The courts of law are our creature and so the courts should be given latitude to make decisions."
Lungu won 50.35 percent of the vote against 47.63 percent for Hichilema.
Hichilema's United Party for National Development (UPND) said on Monday it will appeal the result at the Constitutional Court.
Zambia has been one of Africa's most stable democracies although there were skirmishes during campaigning. The kwacha strengthened 2.5 percent on Tuesday, in a sign investors welcomed an outright winner in the election.
Lungu said there would be work in the next five years of his term in office to revive the flagging economy. "There is no time for a honeymoon," he said.
'COUP ON DEMOCRACY'
Hichilema, popularly known as HH, was not available to comment. His UPND party accused Lungu's party of carrying out "a coup on Zambia's democratic process" in a statement released late on Monday.
"We submitted evidence before the declaration of the results regarding the gross irregularities that have taken place. That is why we will not accept the result," the party said.
The UPND said on Saturday data from its own parallel count showed Hichilema beating Lungu "with a clear margin" with about 80 percent of votes counted. Monday's result means Hichilema has now lost five presidential elections.
The ruling party and the electoral commission have rejected the UPND's charge.
The election was fought around the issues of rising unemployment, mine closures, power shortages and soaring food prices which Hichilema, an economist and businessman, blamed on Lungu's mismanagement.
But Lungu, whose government has been talking to the International Monetary Fund about financial aid to help plug its budget deficit, said he was doing his best to wean the economy off its over-reliance on copper.
Robert Besseling, head of the EXX Africa business risk intelligence group said: "Lungu will struggle to secure concessions from the IMF... and may be forced to turn to Chinese investors to bankroll a recovery of the copper-driven economy."
Chinese companies have invested heavily in mining and other sectors over the last 10 years with investment reaching $2.6 billion in 2014, according to data from the Chinese Embassy.