Police in the Democratic Republic of Congo say five people were killed and 17 police officers injured during outbreaks of violence following the announcement that Felix Tshisekedi won the presidential election.
The runner-up in the election, Martin Fayulu, says the election was rigged and will challenge the result in court.
The Catholic Church, which is very influential in DR Congo, has also suggested there was foul play.
There have been international calls for calm as people wait for the full results to be announced by the electoral commission.
Later on Friday the UN Security Council is due to discuss the Congolese election.