ABUJA, Nigeria (AP) -- Angry opposition supporters in Nigeria's Muslim north set fire to homes bearing ruling party banners Monday and heavy gunfire rang out in several towns as election officials released results showing the Christian incumbent had gained an insurmountable lead.
Results from Saturday's election released live on national television indicated President Goodluck 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 Monday 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 to favor the ruling party.
"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. Election officials said they would finish releasing election results later Monday regardless of the ongoing violence.
Witnesses said youths in the northern city of Kano were setting fires to homes that bore Jonathan party banners. Heavy gunfire also could be heard. An Associated Press reporter there saw hundreds of youths carrying wooden planks in the street, shouting "Only Buhari" in the local Hausa language.
"What I am looking for now is rescue, the mob is still outside. I need rescue," said Mark Asu-Obi, who was trapped inside his Kano home with his wife and three children. "There are hoodlums all over the place. It's not just my place that they are attacking. I am not a politician. I am an independent observer."
In Kaduna, home to the oil-rich nation's vice president, angry young men burned tires in the streets and threw stones at police and soldiers trying to restore order, witnesses said.
"Right now, I'm holed up in my room. There's gunshots everywhere," said Shehu Sani, a civil rights leader. "They are firing and killing people on the street."
Kaduna state police spokesman Aminu Lawal described the fighting there as an "uprising." In neighboring Katsina state, a mob attacked a prison and freed 42 inmates, police spokesman Abubakar Mohammed said.
Federal emergency management agency spokesman Yushua Shuaib declined to release casualty figures out of fears it would further stoke sectarian violence.
"Such a thing can encourage a reprisal attack," he said.
Over the weekend, opposition supporters also rioted in the northeastern state of Gombe. Protesters burned down the house of the local chairman of the ruling party, two hotels and at least two buses there. The rioters accused Gombe's ruling party government of rigging the results to ensure that Jonathan got at least 25 percent of the vote.
Police chief Suleiman Lawal said Sunday that there had been a "complete breakdown of law and order" there.
Nigeria's elections have long been marred by violence and rigging. But voting in the Saturday presidential election had been largely peaceful apart from a hotel blast that wounded eight people and the fatal shooting of a police officer at a polling station.
Nigeria, a nation of 150 million people, is divided between the Christian-dominated south and the Muslim north. A dozen states across Nigeria's north have Islamic Shariah law in place, though the area remains under the control of secular state governments.
Thousands have been killed in Muslim-Christian violence in the past decade, but the roots of the sectarian conflict are often embedded in struggles for political and economic dominance.
Jonathan, who became president after his Muslim predecessor died in office last year, has long been considered the front-runner. His ruling People's Democratic Party has dominated politics in the West African giant since it became a democracy 12 years ago.
However, the country's Muslim north remains cold to Jonathan as the Christian from the south who took over after the death of the country's elected Muslim leader.
Many of the north's elite wanted the ruling party to honor an unwritten power-sharing agreement calling for a Muslim candidate to run in this election, yet Jonathan prevailed in the party's primary.
Associated Press writers Maggie Fick and Salisu Rabiu in Kano, Nigeria; Krista Larson in Lagos, Nigeria; Bashir Adigun in Abuja, Nigeria and Saadatu Mohammed in Gombe, Nigeria contributed to this report.