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.