In one of his first statements since the December 30 vote, Fayulu urged the authorities to publish who had won.
“The Congolese people already know the result,” he said, warning against political tensions.
The elections, postponed three times over the last two years, were to choose a successor to long-term President Joseph Kabila but the provisional results, due last Sunday, have been delayed.
The Independent National Electoral Commission (CENI) has said it is having problems collecting the data.
Fayulu’s statement came as the main opposition party UDPS claimed on Tuesday that its candidate Felix Tshisekedi had won and that a meeting with Kabila was being prepared.
“The two figures have an interest in meeting to prepare a peaceful and civilised transfer of power,” said UDPS secretary general Jean-Marc Kabund.
Talk of a possible rapprochement between the UDPS and Kabila was also fuelled after Tshisekedi told Belgian newspaper Le Soir the president could be honoured for his behaviour after stepping down.
“One day we will even have to think of paying tribute to him (Kabila) for agreeing to withdraw,” Tshisekedi said in an interview.
Of the three main contenders for president, Kabila has backed Emmanuel Ramazani Shadary as his preferred successor.
– ‘Results not negotiable’ –
But as the other key opposition candidate, Fayulu in his statemen warned the electoral commission “against any attempt to disguise the truth of the polls”.
CENI must “publish the provisional results of the presidential election in the near future,” he said.
According to the initial timetable, after provisional results are released, definite results are due on January 15 with the swearing-in of the new president three days later.
The DRC has a long history of political violence and suspicions of political manipulation and electoral fraud run deep.
It has never experienced a peaceful transition of power since gaining independence from Belgium in 1960.
CENI has said it postponed the results announcement as it was still counting ballot papers.
Fayulu accused CENI of knowing the “real results”, saying it had “deliberately abstained from making them public in violation of its own timetable for unacknowledged reasons”.
“The election results are not negotiable,” Fayulu said, also speaking on behalf of five other minor candidates.
– ‘Truth and justice’ –
The Protestant Church also added its voice on Tuesday to that of the Catholic Church in urging the authorities to publish the results.
In a statement, the Church of Christ in Congo (ECC) appealed to the election commission to “uphold its promises, made before God and before the nation, to offer the nation the truth, and nothing but the truth, of the ballot box.”
Last Thursday, the powerful Roman Catholic Church said it knew who had won the ballot from its own monitors at polling stations.
It called on CENI “to publish the election results in keeping with truth and justice.”
The Catholic Church’s National Episcopal Conference of Congo (CENCO) said it had deployed more than 40,000 observers around the vast country.
Catholicism is the main religion in DRC. The ECC, the largest Protestant church, said it had 10,000 election observers on December 30.
The coalition of governing parties, the Common Front for Congo (FCC), has accused CENCO of bias and breaching electoral law. FCC has accused Fayulu of trying to put pressure on the CENI.
Fayulu is backed by former Katanga governor Moise Katumbi, considered a “Judas” by Kabila, and ex-warlord and former vice president Jean-Pierre Bemba.
DR Congo suffered two wars between 1996 and 2003 that claimed millions of lives through bloodshed, fighting, starvation and disease.
Bloody clashes also marred elections in 2006 and 2011.