Nigeria's opposition and independent monitors says the country's presidential election is deeply flawed.
The two main opposition candidates say Saturday's vote was marred by widespread irregularities. One of the candidates, Vice President Atiku Abubakar, called for the annulment of the vote, describing it as the worst election ever in the country.
The US-based monitoring group, International Republican Institute, said the vote did not meet international standards. It reported ballot stuffing, police intimidation, and group voting.
The European Union presidency also expressed concerns, saying Nigerians were not able to vote freely and without fear.
A Nigerian election observer group (Transition Monitoring Group) called for the election to be re-run. It said polls opened very late in some of Nigeria's 36 states and failed to open at all in others.
Election results are due to be released starting Monday.
Journalists also reported cases of blatant vote rigging in favor of the ruling People's Democratic Party candidate, (Katsina State Governor) Umaru Yar'Adua.
Scattered violence was reported throughout Nigeria Saturday. Police opened fire on demonstrators protesting against alleged vote-rigging in the northern town of Daura, killing at least three people.
Electoral Commission Chairman Maurice Iwu acknowledged some problems with the vote, but said the commission performed creditably well, given the circumstances.
The presidential election is meant to bring about the first handover from one civilian leader to another since Nigeria gained independence from Britain in 1960. Voters also cast ballots Saturday to fill 300 seats in the federal legislature.
Nigerian President Olusegun Obasanjo is due to step down next month after serving two four-year terms.