KINSHASA (Reuters) - Results from Democratic Republic of Congo’s chaotic presidential election could be delayed past Sunday’s deadline because counting centers are still waiting for more than 80 percent of local tallies, the electoral commission said.

The election, which is meant to mark Congo’s first democratic transfer of power, has already been marred by violence and logistical problems. The opposition has said there was widespread fraud, an accusation dismissed by the government.

As of Wednesday - three days after the election - counting centers had received just 17 percent of the tally sheets drawn up by individual polling stations, the president of the CENI electoral commission, Corneille Nangaa, told Reuters.

“We will try as hard as possible to meet Sunday’s deadline, but it will be challenging,” Nangaa said. He did not say what was causing the delays.

A spokesman for Felix Tshisekedi, one of two opposition candidates, said the hold-up was a further sign of fraud. “They are clearly trying to prolong the process to manipulate the truth of the ballots,” said Vidiye Tshimanga.

There was no immediate reaction from the government, though regional monitors earlier said the Dec. 30 vote was “relatively well-managed” given the challenges involved.

The election allowed “the majority of the Congolese population to exercise its right to vote,” the Southern African Development Community (SADC) said.

Vote counting was transparent, 59 percent of polling places it observed opened on time and police securing the polls behaved professionally, the organization added.

“A FIRST GREAT VICTORY”

Approval of the election’s results by SADC powers such as South Africa and Angola will be critical for the legitimacy of the administration of the next president, who will succeed veteran incumbent Joseph Kabila on Jan. 18.

Angola and South Africa have been important allies of Kabila over the years, but relations were strained by his refusal to step down when his mandate officially expired in 2016.

Pre-election polling showed Kabila’s preferred candidate, ex-interior minister Emmanuel Ramazani Shadary, trailing the main opposition candidates, Martin Fayulu and Felix Tshisekedi, but both sides say they expect to win.

An African Union observer mission said in a separate statement on Wednesday that election day was blighted by a number of logistical problems.

“The holding of these elections constitutes, in itself, a first great victory for the Congolese people,” it said. “The mission strongly wishes that the results that will be declared are true to the vote of the Congolese people.”

Kabila’s government refused to accredit election monitors from the European Union and the U.S.-based Carter Center, which said there were widespread irregularities in the 2011 election.

Contested election results in 2006 and 2011 led to violent street protests, and a disputed outcome this time could also destabilize Congo’s volatile eastern borderlands with Rwanda, Uganda and Burundi, where dozens of militia groups are active.