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Lagos, Nigeria (CNN) -- President Goodluck Jonathan pledged a "new dawn" for Nigeria, days after the electoral commission declared him the winner in a vote hailed as a significant improvement from past polls.
The last election four years ago was widely condemned for rampant vote rigging, violence, theft of ballot boxes and intimidation.
Though marred by violence, reports of underage voting and logistical problems, observers considered the latest election an improvement.
"This time around, one of the differences is that both local and international observers said, 'Yes, there is significant departure from the past, '" Jonathan told CNN.
World leaders declared the vote a success, but urged election officials to probe allegations including ballot stuffing and unusually high turnout in some areas.
"This historic event marks a dramatic shift from decades of failed elections and a substantial improvement over the 2007 presidential election," U.S. Secretary of State Hillary Clinton said in a statement.
British Foreign Secretary William Hague described the vote as a "significant step forward" for the nation.
Jonathan said the vote ushers a new era for Africa's most populous nation and its biggest oil producer.
"That should tell you that what we are saying, we are going to do it and this is a new dawn," the president said. "We are going to work with all Nigerians to make sure that changes are made."
Jonathan hails from the oil-rich southern part of Nigeria, an area that is majority Christian.
Parts of the mostly Muslim north plunged into chaos after it became apparent that Jonathan had won, charging that the elections were rigged.
Rioters prowled the streets in the north, shouting the name of Gen. Muhammadu Buhari, a former military ruler and the main opposition candidate.
About 17,000 people fled their homes in the region as violence flared, the Nigerian Red Cross said.
Jonathan appealed for unity as the unrest sounded alarms for the government, prompting it to deploy the military and enforce curfews to maintain calm.
"My brothers and sisters, we are all winners," Jonathan said earlier in the week. "In this context there is no victor and no vanquished. We have demonstrated, even in our diversity, the progress of Nigeria remains paramount for all."
An investigation is under way to determine the perpetrators of the violence, which the president attributed to jobless youth.
"We've been having a crisis in the north, we've been having a crisis in the south, all the symptoms are the same,"he told CNN. "We have a number of young people that have no source of income that we must provide."
If the government does not help provide a source of income, he said, the youth are at risk of being paid to spark violence.
He declined to get into specifics on the perpetrators of the violence.
"The government will find out formally," he said. "If I make some statements, I will be biased in the minds of people and I don't want to accuse anybody."
Nigeria's elections, staggered over three weeks, conclude with the vote for governors April 26.
CNN's Christian Purefoy contributed to this report.