Officials in the Democratic Republic of Congo say the incumbent Joseph Kabila has won the fiercely contested presidential election, but his main rival has rejected the result.
Provisional results show he picked up 49% of votes cast, compared with 32% for his main rival Etienne Tshisekedi.
The result must now be confirmed by the Congolese Supreme Court.
However, Mr Tshisekedi was quick to reject Mr Kabila's win, citing election fraud, and declared himself president, the BBC reports.
He has urged his supporters to remain calm but, should he decide to call them on to the streets, there are fears there could be violent clashes with the police and army.
The country is already the scene of the UN's largest peacekeeping operation and the BBC says that now international mediators might be needed to ensure it does not plunge the volatile Central African nation into an even deeper crisis.