Early results in Nigeria's presidential election have given a healthy lead to incumbent President Olusegun Obasanjo. With about one-fifth of the ballots counted, he leads with more than 70 percent of the vote, while his closest rival has about 25 percent. The winner could be declared as early as Monday.
The early results gave Mr. Obasanjo a significant lead over his main challenger, Muhammadu Buhari. But the first results came mainly from southern parts of the country, and Mr. Buhari's support is expected to be strongest in the north, where he comes from.
Results are streaming in fast, and the head of the Nigerian electoral commission says he could declare a winner sometime Monday. But tensions are running high in several parts of the country, and Mr. Buhari's party is already crying foul. Senior party officials are alleging there was "massive rigging" of the vote.
Mr. Buhari last week said he would call for "mass action" if he thought the election was stolen.
Violence disrupted voting on Saturday in the southeast Niger Delta region, and international election observers say they are very concerned about the way the election was carried out in Rivers State.
Observers and journalists in the region say many polling stations never opened in Rivers State and nearby Delta State, and opposition supporters largely boycotted the election. But the electoral commission is reporting a high turnout in the area, raising suspicions of fraud.
Even if Mr. Obasanjo wins a majority nationwide, he could be forced into a runoff if he fails to get enough support in the northern states, Mr. Buhari's stronghold.
Nigeria has a complex electoral system. A candidate has to win not just a simple majority of the overall votes, but also at least 25 percent of the votes in two-thirds of the states. The system is designed to make sure the eventual winner has support throughout the nation, not just in one region.
Election officials have already declared the winners of a number state governors' races. Candidates from Mr. Obasanjo's party have done better than expected in the northern states, which could indicate he will get the support he needs to win in the first round. But it could also anger opposition candidates, who have already accused the ruling party of trying to steal the election.
One of the biggest surprises so far came in the governor's race in Mr. Buhari's home state of Katsina, where the candidate from Mr. Obasanjo's party won by a relatively wide margin.
This is Nigeria's second democratic election since the end of military rule in 1999. The country's last civilian-run election was nearly 20 years ago. That poll was widely condemned as flawed, and the government was overthrown by a military coup several months later.
Nigeria is sharply divided along ethnic and religious lines. The north is largely Muslim while most of the southerners are Christian or Animist.