Zambian President Edgar Lungu narrowly won re-election on Monday, in a vote his main rival Hakainde Hichilema rejected on claims of alleged rigging by the electoral commission.
Lungu faced a tough challenge from Hichilema to rule over Africa's second-largest copper producer, which has suffered from an economic slump due to depressed commodity prices.
Lungu, who narrowly beat Hichilema in a vote last year to replace late president Michael Sata, won 50.35 percent of the vote, against 47.63 for his opponent, the Election Commission of Zambia (ECZ) said.
"I honorable Justice Esau Chulu, being the returning officer for the election, declare Edgar Chagwa Lungu president elect," the ECZ chairperson said.
Lungu's supporters, draped in the regalia of the ruling Patriotic Front (PF), took to the streets, chanting slogans and hooting car horns in celebration soon after the announcement.
But Hichilema's United Party for National Development (UPND) accused electoral officials of colluding in favor of Lungu since vote counting started on Thursday night and said it would appeal the result at the Constitutional Court.
"We have evidence to the effect that the votes for Hakainde Hichilema have been deliberately reduced in collusion with the Electoral Commission of Zambia," party lawyer Jack Mwiimbu told journalists.
"We have confidence that the constitutional court will rise above board and declare the results a nullity."
The commission and Lungu's PF have both rejected the UPND's charges.