Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. Riots Break Out in Northern Nigeria As President Declared Winner VOA News April 18, 2011 Incumbent Nigerian President Goodluck Jonathan casts his ballot in Otuoke, April 16, 2011 Photo: Reuters Incumbent Nigerian President Goodluck Jonathan casts his ballot in Otuoke, April 16, 2011 Election officials in Nigeria Monday declared President Goodluck Jonathan the winner of the nation's presidential election, as riots broke out in the mainly Muslim north to protest the outcome. Officials say Jonathan received more than 22 million [22,495,187] votes in Saturday's polls, nearly twice the number of his main challenger, former military ruler Muhammadu Buhari, who garnered about 12 million [12,214,853]. Jonathan won enough votes to avoid a run-off. A candidate must win a simple majority and at least a quarter of the vote in 24 states. Jonathan won 57 percent of the votes cast. News of Jonathan's win sparked riots across Nigeria's northern region. The Nigerian Red Cross estimated that more than 270 people have been wounded and another 15,000 displaced by the violence. Opposition supporters claimed the vote was rigged and they set fire to homes, burned tires and hurled rocks at police to protest the results. Many in the Muslim-majority north backed Buhari, a Muslim. Jonathan, a Christian, dominated the mostly Christian south. Jonathan appealed for an end to the violence Monday. He called on political leaders to urge their supporters to refrain from any violence. The Red Cross said field workers responding to the election violence bypassed bodies in order to rush the injured to hospitals, particularly in Kaduna and Kano states. A 24-hour curfew was imposed in Kaduna state, where angry rioters clashed with police and set homes on fire in the cities of Kaduna and Zaria. In the capital of Kano state in the city of Kano, security forces fired shots into the air as stone-throwing youths took to the streets and chanted support for Buhari. Observers have said Saturday's vote proceeded calmly, with few instances of cheating. Jonathan has promised to improve the country's economy, health and education. He assumed the presidency last year following the death of his predecessor, Umaru Yar'Adua. Some information for this report was provided by AFP, AP and Reuters. .