Nigeria's main opposition challenger, former military ruler Muhammadu Buhari has a lead over incumbent President Goodluck Jonathan after more than half of Nigeria's 36 states have declared following Saturday's elections.
General Buhari's All Progressives Congress is ahead by around two million votes. A victory for General Buhari would make President Jonathan, who heads the People's Democratic Party, the first incumbent to lose an election in Nigeria.
More than 800 people were killed in violence that followed a previous election in 2011 between the two men.
Election monitors have expressed concern over voter irregularities. Hannah Roberts is deputy chief observer for the European Union.
IN: "We saw some ...
OUT: ..arriving intact."
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