Democratic Republic of Congo's police dispersed a gathering on Monday of supporters waiting to hear a speech by presidential runner-up Martin Fayulu, his spokesperson said.
Dozens of people gathered outside his coalition's headquarters in Kinshasa before police arrived and cancelled the event, said Eve Bazaiba.
"Our headquarters (HQ) was besieged, our activists began to gather, we began to climb the podium on which our leader should speak, and the police came and took the podium and the speakers," she said, adding that police had also blocked the entrance and exit gates at the headquarters.
She dismissed calls by declared president-elect Felix Tshisekedi to work together for reconstruction of DRC.
"We cannot work together in irregularities," she said. "We cannot build on falsehoods ... we want to know the truth of the ballot box first."
The Constitutional Court on early Sunday refused Fayulu's request for a vote recount and reaffirmed the victory of Felix Tshisekedi in the presidential race, saying he received 38% of the vote, while Fayulu received 34%.
In his legal challenge, Fayulu said he won 60% of the vote according to leaked commission results. The 40 000 person Catholic Church observation mission also affirmed that results from polling stations showed that Fayulu was the clear winner. But the court said that Fayulu did not provide evidence proving his claim.
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Rejecting the court's decision, Fayulu declared that he is Congo's "only legitimate president" and called for the Congolese people to peacefully protest what he called a "constitutional coup d'etat."
DRC's government has called Fayulu's statements "a shame," and irresponsible.
"We want the truth of the polls, they stole Fayulu's victory," said Jacques Nzita outside Fayulu's headquarters.
Fayulu on Monday called on African presidents to listen to the voice of DRC people.
"To African presidents who demand the Congolese to respect the Constitutional Court decision, I ask you to respect the sovereign decision of the Congolese people who elected me president with more than 60 percent," he wrote on Twitter. "Don't encourage fraud, lies and forgery."
The African Union, which had noted "serious doubts" about the vote and made an unprecedented request for DRC to delay the final results, postponed its urgent mission to DRC planned for Monday.
DRC is on the brink of its first peaceful, democratic transfer of power since independence in 1960.
Tshisekedi's inauguration, which was planned for Tuesday, is now postponed, government spokesman Lambert Mende told The Associated Press. He did not give reasons for the delay, but said it will likely take place Thursday.
Also Monday, RFI, CCTV and the television station for opposition leader Jean-Pierre Bemba came back on the air after being cut two days after December elections. Internet, also cut before the election, had slowly returned in recent days.