Riots erupted across northern Nigeria today after President Goodluck Jonathan secured enough votes to win last Saturday's presidential election.

Many in the north backed the top challenger, Muhammadu Buhari, a Muslim and former military ruler.

According to the daily newspaper Leadership in Abuja, Buhari said that overnight there were ?airplanes carrying ballot papers to some of the states,? where they were being illegally thumb-printed. 

People holding wooden and metal sticks demonstrate
People holding wooden and metal sticks demonstrate in Nigeria's northern city of Kano where running battles broke out between protesters and soldiers on Monday.

Reuters quotes a Buhari supporter, former government minister Nasir el-Rufai, as saying, ?No real elections took place in the south-east and south-south? regions. He said the opposition would prove the charges ?in due course.?

So far, Buhari?s statements cannot be verified, said Clement Nwankwo, the executive director of the Policy and Legal Advocacy Center in Abuja.

?I don?t know where (Buhari) got his information from,? said Nwankwo. ?We cannot verify the allegation that a plane was ferrying ballot papers to Katsina and stuffing ballot boxes. But we do know that there were different complaints of electoral malpractice that cuts across all of the political parties as well and across different parts of the country.?

Nigerian Civil Society Urges Calm in Wake of Elect
Nigerian Civil Society Urges Calm in Wake of Electoral Violence

General Buhari has said he would not pursue official complaints, though newspapers across Nigeria today said his political party, the Congress for Progressive Change, may well do so.

Nwankwo?s center is one of nearly two dozen groups that have come together to form what they call a ?situation room? that is monitoring the polls. In the wake of violence in the north, he said his and other groups are urging the public to remain calm.

?We are emphasizing the need to respect the sanctity of the electoral process and the [legal] remedies,? he said, ?and ?we are urging the leading candidates and civic leaders to join in the appeal for calm among the citizens.