Felix Tshisekedi has vowed to be the president "of all Congolese" after the Democratic Republic of Congo's (DRC) electoral commission declared him the winner of the country's long-delayed elections.
The result, which was announced in the early hours of yesterday, was rejected by rival, Martin Fayulu, who was backed by opposition heavyweights and had led in polling prior to the December 30 vote.
France and Belgium are challenging the result, with France's foreign minister saying that Tshisekedi was "not consistent" with the results and that his rival, Martin Fayulu appeared to have won.
In remarks made just hours after the provisional results were announced, France' Foreign Minister, Jean-Yves Le Drian said Tshisekedi's opposition rival Fayulu, who was declared the runner-up, should have been declared the winner.
"It really seems that the declared results are not consistent with the true results," he told France's CNews channel. "On the face of it, Mr Fayulu was the leader coming out of these elections."
In a country which has never known a peaceful handover of power since gaining independence from Belgium in 1960, Le Drian called for calm.
He said DR Congo's powerful Catholic Church, which deployed more than 40,000 observers to monitor the elections, knew who had really won the vote with their observations suggesting a win for Fayulu.
"CENCO (National Episcopal Conference of the Congo) carried out an inspection and declared a result which was totally different," he said, referring to the body representing the country's Catholic bishops.
In a statement released on Thursday, the church said that "the results of the presidential election published (by the electoral commission) do not match those collected by our observer mission."
The African Union called for any dispute over the Democratic Republic of Congo's election result to be resolved in a peaceful manner, through dialogue.
The Belgian Foreign Minister, Didier Reynders also cast doubt on the election result, saying his country would use its temporary seat on the UN Security Council to seek clarification about Tshisekedi's surprise victory.
Mr. Fayulu dismissed the outcome as an "electoral coup".
Emmanuel Ramazani Shadary, the hand-picked candidate of long-time President Joseph Kabila, was third with about 4.4 million votes.
Barnabe Kikaya Bin Karubi, one of Kabila's top advisers, accepted the loss of the ruling party's preferred candidate.
"Of course we are not happy as our candidate lost, but the Congolese people have chosen and democracy has triumphed," Kikaya told Reuters news agency shortly after Tshisekedi was declared the winner.
Tshisekedi had won with 38.57 per cent of more than 18 million ballots cast, Corneille Nangaa, head of the election commission said.
Tshisekedi received more than seven million votes compared with about 6.4 million for Fayulu, who had warned against manipulation.
Emmanuel Ramazani Shadary, the hand-picked candidate of long-time President Joseph Kabila was third with about 4.4 million votes.
Some observers have suggested that Kabila's government sought to make a deal as hopes of a win for Shadary faded.
Tshisekedi, 55, is the son of the late Etienne Tshisekedi, the face of the DRC's opposition for decades.