President Muhammadu Buhari took an early lead on Monday in initial official results from Nigeria's presidential election but the party of his main challenger quickly rejected the tallies as "incorrect and unacceptable".
Saturday's election was expected to be Nigeria's tightest since the end of military rule two decades ago.
At stake is control of Africa's top oil producer and biggest economy. Northeast Nigeria has also suffered from a decade-long battle with Islamist militants, which has spilled into neighboring countries and led to the deployment of a regional task force.
Buhari, 76, is a former military ruler seeking a second term on an anti-corruption platform, while Atiku, 72, a businessman and ex-vice president, has pledged above all to expand the role of the private sector.
The chairman of Atiku's People's Democratic Party (PDP), Uche Secondus, talks to reporters as he rejects initial election result, in Abuja, February 25, 2019. /VCG Photo
Initial results released by the Independent National Electoral Commission (INEC) on Monday put Buhari in the lead, having won in seven of Nigeria's 36 states, the commission said.
Atiku prevailed in two states and the capital Abuja, which is not a state but treated as a separate district in elections.
In provisional results announced in state capitals but not yet confirmed by the commission, Buhari and Atiku each won in two states.
Asked about the early results, Buhari told reporters: "I don't want to depend on rumors...We will rather wait for INEC to announce the (full) results."
But the chairman of Atiku's People's Democratic Party (PDP), Uche Secondus, said the election tallies announced so far were "incorrect and unacceptable".
Supporters of the All Progressives Congress (APC) led by President Muhammadu Buhari celebrate after initial results were released by the Nigerian Independent National Electoral Commission (INEC) in Kano, February 25, 2019. /VCG Photo
The outcome, not expected until later in the week, appears to hinge on which man voters trust most to revamp an economy still struggling from a 2016 recession.
A credible and relatively calm vote would open a new chapter in the chequered political history of Nigeria, where nearly six decades of independence have been tarnished by military coups, endemic corruption and secessionist movements.
But doubts rose when the election was postponed on February 16, just hours before it was due to begin, with authorities citing problems in delivering ballot papers and results sheets.