Nigerians vote for president Saturday as Africa's most populous nation seeks to end its history of flawed elections.
President Goodluck Jonathan of the ruling People's Democratic Party (PDP) is favored to win. However his top rivals are reported to be considering an alliance that could force a run-off.
Officials say talks have been held between the parties of main opposition candidates Muhammadu Buhari and Nuhu Ribadu.
Supporters say one possibility is for Ribadu, a former anti-corruption chief, to step aside and allow Buhari, a former military ruler, to run as the alliance's candidate.
Buhari, a Muslim, has strong support in the predominantly Muslim north. Jonathan, a Christian, has strong support in the mostly Christian south.
Meanwhile, partial results from parliamentary elections last Saturday indicate Nigeria's ruling party has lost ground, but will still keep its majority.
With more than 70 percent of the votes counted, the PDP has won 59 Senate seats compared to 32 captured by all the opposition parties. The ruling party has captured 140 seats in the House of Representatives, while the opposition has won 123.
Parliamentary polling was delayed until this coming Saturday at 15 percent of the polling stations because of a shortage of ballots.
International monitors say the polls that took place last Saturday were "generally peaceful" and "encouraging."
The European Union declared Nigeria's last elections in 2007 "not credible" because of widespread fraud, violence and major organizational problems.
Saturday's elections went ahead after two postponements and in spite of bombings at election-related sites in the cities of Maiduguri and Suleja.
Some information for this report was provided by AFP and Reuters.