African Union Commission chief Moussa Faki Mahamat failed to congratulate opposition challenger Felix Tshisekedi, whose surprise victory with 38 percent of the vote was announced by the country's electoral commission, CENI, on Thursday.
"It is important that any disagreement over the proclaimed results, notably that they did not reflect voters' wishes, be resolved peacefully," the AU head said in a statement.
The reaction of South Africa's President Cyril Ramaphosa was also restrained. In a statement, Ramaphosa said he had "noted" the provisional results, reserving his congratulations for those who had ensured "peace and stability" during the election process.
The provisional results are disputed, with the country's highly regarded Catholic church saying its findings from 40,000 election monitors at polling stations showed a different winner. The church has said it is unable to name a victor under election law. However, opinion polls before the vote indicated a landslide victory for opposition candidate Martin Fayulu, whom CENI named as the runner-up with 34.8 percent.
Fayulu accuses Tshisekedi of making a power-sharing deal with outgoing President Joseph Kabila and CENI of rigging the vote in Tshisekedi's favor.
Europe calls for clarification
Germany's relationship with Congo is cool – two years ago, the German government postponed aid payments to the country because of delays to the election, which were supposed to take place in 2017.
Now the election has finally been held, Germany's reaction was muted. The Federal Foreign Office said it had "taken note" of the provisional results and "of the fact that these results have been contested by parts of the opposition."
Elsewhere in Europe, doubts about the legitimacy of Tshisekedi's win were stronger. British Foreign Secretary Jeremy Hunt tweeted that he was "very concerned about discrepancies" while France's foreign minister Jean-Yves Le Drian called for "clarity" on the results as they are "opposite to what we expected."
This was echoed by the United States who also demanded "clarification".
Fayulu claims 61 percent of the vote
Speaking before hundreds of his supporters in Kinshasa on Friday, Fayulu said that he had seen the Catholic church's independent vote tally. Based on these figures, he said he had won 61 percent of the presidential vote – trouncing Tshisekedi who only garnered 18 percent.
Earlier, Fayulu, a businessman and vocal campaigner against Congo's widespread corruption, told DW the election results had "nothing to do with reality."
"Mr. Tshisekedi has been appointed by the will of Mr Kabila and we cannot accept the making of a plot against the people."
Kabila has ruled resource-rich Congo for nearly 18 years, assuming power after the assassination of his father in 2001. The Kabila family control almost all sectors of Congo's economy through a veritable empire of more than eighty companies inside and outside the country, from telecommunications to mining.
With Kabila constitutionally barred from running for a third term, many believed he would ensure the victory of his hand-picked successor and the ruling party candidate, Emmanuel Shadary. Shadary, however, performed badly in the December 30 election, coming a distant third.
Handing over the presidency, but not necessarily power
Emerie Damien Kawira, the president of the Congolese Coalition for Transition, a Brussels-based opposition group, told DW they had "credible information" that Kabila and Tshisekedi had signed an agreement. As part of the deal, the new "prime minister will come from Kabila's party and his camp will still head the finance and security dockets."
"That shows that Kabila still intends to remain in power," Kawira said.
According to Reuters, Tshisekedi's camp has acknowledged contact with Kabila's representatives but denies there has been any deal, saying talks were aimed only at ensuring a peaceful handover of power.
This could be Congo's first peaceful, democratic transfer of power since independence from Belgium in 1960, after decades of coups, dictatorship, assassinations and civil wars. But observers have warned that a court challenge to the results could spin the long-troubled country into chaos.
"We will go out on the streets and use all our power to show that we reject these results," said Fayulu supporter Gauthier Ipuka. The 28-year-old unemployed member of Fayulu's Lamuka party told DW that protests were being coordinated throughout the country for Saturday.
"We won't allow this game between Kabila and Tshisekedi," he said.
Fayulu has announced he would file a court challenge to the official vote results on Saturday morning.
"Those who have been silly enough to publish false results, we will challenge them," he said.
Some Fayulu supporters, however, are worried that the constitutional court could invalidate the election results, keeping Kabila in power until a new vote.
Jacob Bomani in Brussels, Wendy Bashi and Jonas Gerding in Kinshasa, Daniel Pelz in Berlin and Frejus Quenum in Bonn contributed to this article.