Nigerian President Goodluck Jonathan has appealed for an end to "unnecessary and avoidable" post-election violence across the north of the country.
Mr Jonathan has emerged as a clear winner in the presidential poll with about 57pc of the votes cast.
He secured 22.5 million votes compared to 12.2 million votes, or 31pc, won by his nearest rival Muhammadu Buhari.
Earlier yesterday angry opposition supporters in Nigeria's Muslim north set fire to homes bearing ruling party banners, and heavy gunfire rang out in several towns as election officials released results showing the Christian incumbent had gained an insurmountable lead.
The violence cut across 13 states, leaving people hiding in their homes. Many expected casualties, though federal officials refused to provide any figures. However, the Nigerian Red Cross said that 276 had been wounded and 15,000 displaced.
Results from Saturday's election released on national TV indicated President Jonathan had a commanding lead of more than 10 million votes with only two states left to be announced. The Muslim north had largely voted for former military ruler Muhammadu Buhari.
Buhari's party brought a formal complaint yesterday afternoon to the nation's electoral commission over vote tallies, alleging massive rigging in Jonathan's homeland. The letter also alleged that the computer software used to tally results had been tampered with in northern states.
"What is being exhibited to the world is not collated from polling units but . . . a lot of manipulations," the letter read.
In a statement, the federal police blamed the violence on "persons who failed to accept the results", denying it came from religious or ethnic roots.
Witnesses said youths in the northern city of Kano were setting fires to homes that bore Jonathan party banners. Gunfire also could be heard.
One reporter there saw hundreds of youths carrying wooden planks in the street, shouting "Only Buhari" in the local language.