Former military ruler Muhammadu Buhari has become the first opposition candidate to win presidential elections in Nigeria.
Gen Buhari’s party said his opponent, incumbent Goodluck Jonathan, had admitted defeat and congratulated him.
Mr Jonathan trailed Gen Buhari by about two million votes when he conceded.
Observers have generally praised the election but there have been allegations of fraud, which some fear could lead to protests and violence.
“President Jonathan called General Muhammadu Buhari, the winner of the elections, to congratulate him,” Lai Mohammed, a spokesman for Gen Buhari’s All Progressives Congress (APC), said.
The spokesman praised Mr Jonathan, saying: “He will remain a hero for this move. The tension will go down dramatically.”
“Anyone who tries to foment trouble on the account that they have lost the election will be doing so purely on his own,” he added.