The Democratic Republic of the Congo’s (DRC) presidential election is facing a crisis of legitimacy amid opposition calls for the vote to be annulled due to alleged fraud.

Five opposition candidates, including former provincial Governor Moise Katumbi, said on Saturday the vote should not stand as it had been tainted by “massive fraud.”

Five other opposition leaders, including Nobel Peace Prize laureate Denis Mukwege and former oil executive Martin Fayulu, have called for a protest march against the result next Wednesday.

“We will protest against the irregularities noted during the voting operations,” they said in a letter to the governor of Kinshasa, where they plan to rally.

About 44 million people in the mineral-rich Central African nation were registered to vote in the elections to choose the country’s president, national and regional lawmakers, and local councilors.

President Felix Tshisekedi, who had a sizeable lead in preliminary results of voting by diaspora voters, is running for re-election against 18 opposition candidates.

Western governments have called for restraint amid fears of a repeat of the violence that has followed disputed election results in the past.

In a joint statement on Saturday, 12 European embassies and the Canadian embassy called for restraint.

“As the vote counting continues, we urge all stakeholders, especially political actors, candidates and their supporters, to exercise restraint, allow the process to unfold, and raise their concerns peacefully,” the embassies said.

The vote has been marred by accusations of corruption and chaotic organization since it kicked off on Wednesday, with authorities extending the poll into Thursday after some polling stations failed to open and some voters could not find their names on registers.

While electoral authorities officially extended the vote until Thursday, ballots were still being cast on Saturday in remote areas.

The unscheduled extension prompted fierce pushback from opposition candidates, some of whom labeled the move unconstitutional and called for a new election.

Independent observers have raised concerns about the vote, with the United States-based Carter Center describing “serious irregularities” at 21 out of 109 polling stations it visited and noting “a lack of confidence in the process”.

The DRC, which is one of the world’s poorest countries despite holding vast reserves of copper, cobalt and gold, has a history of election-related violence.

At least 19 people were killed in election-related violence in the run-up to the vote.

Tshisekedi’s election as president in 2018 was also marred by accusations of fraud.

At least 34 people have been killed and 59 others wounded in protests related to the vote, according to the United Nations.