Opposition leader Muhammadu Buhari has opened up a slight lead over President Goodluck Jonathan in a tight Nigerian election that looks set to go down to the wire.
Results from Nigeria's elections, potentially the closest contest since the end of military rule in 1999, trickled in on Monday after a weekend vote marred by confusion, arguments and sporadic violence.
After announcing results in 18 states and the Federal Capital Territory (FCT), the Independent National Electoral Commision (INEC) suspended the announcement of results late on Monday night local time - saying that they would start again at 09:00 GMT on Tuesday morning.
The electoral commission announced that the opposition All Progressives Congress (APC), the party of presidential challenger Buhari, took the most votes in Oyo, Kogi, Kwara, Katsina, Kaduna, Osun, Kano, Jigawa and Ondo states.
NIGERIA DECIDES: Read more of our special coverage of the closest race in years
President Jonathan's ruling PDP took the most votes in Nasawara, Ekiti, Enugu, Abia, Imo, Akwa Ibom, Plateau and Anambra states and the FCT.
Buhari was leading the overall vote count by more than two million votes. Results from each of the 36 federal states plus the FCT were being tallied at the International Conference Centre in Abuja, t he capital.
To win the election, a candidate needs to win more than 50 percent of the total votes nationally - and take at least 25 percent of the vote in two thirds of the states.
On Sunday, protesters in Rivers state, the headquarters of Africa's biggest oil industry, declared the voting as fraudulent.
The United Nations and the African Union, which both had election observers on the ground, said the vote in Africa's most populous nation was broadly in line with "continental and regional principles".
"The AUEOM (African Union Election Observation Mission) encourages all parties to resort to legally established channels, should there be a dispute on the outcome of the process," it said in a statement.
"The AU long-term observers will continue to observe the post-electoral process."
The election pits President Jonathan, 57, against 72-year-old former military ruler Buhari for the favour of an electorate divided along a complex mix of ethnic, regional and in some cases religious lines.
|Women show their new electoral cards while queuing at a accreditation centre in Abuja [AFP]
Even before preliminary tallies were recorded, the opposition APC rejected the process in Rivers state and denounced the vote there as "a sham and a charade".
"Whatever trash will [be] announced as the result of today's election is not acceptable to us," it said.
"There was no election in Rivers," Achinike William-Wobodo, a polling agent for the APC said, calling for a re-vote.
'Appeal to all Nigerians'
In a sign the opposition will challenge results elsewhere, the APC governor of the southern Imo state, Rochas Okorocha, denounced on television the conduct of the election in his region and accused the military of meddling in the result.
Attahiru Jega, INEC chairman, said he was concerned about the Port Harcourt complaints, which alleged that opposition agents were kicked out of vote-tallying meetings, and had launched an investigation.
In Kaduna, the northern city worst-hit by the 2011 post-election violence, the streets were virtually devoid of traffic and many shops were shuttered.
Voting was pushed into an unscheduled second day on Sunday after failures in controversial new technology designed to "read" biometric identity cards to combat electoral fraud.
Among those whose card did not work was the president himself.
But election chief Attahiru Jega said his commission was confident its objective of holding a "free, fair, credible and peaceful" election was "on course".
"We appeal to all Nigerians to remain peaceful as they await the return of these results," he told a news conference on Sunday.
Boko Haram has dominated the campaign, with military operations against the rebels forcing a six-week delay to the scheduled February 14 election.
On Sunday, residents and a military source said soldiers supported by two fighter jets intercepted the fighters at Dungulbe village, 7km from Bauchi city in the northeast.
A spokesman for the Bauchi state governor said an indefinite, round-the-clock curfew had been imposed on three areas because of the fighting.
The rebels were believed to have come through the town of Alkaleri, 60km away, where there was a dawn raid on Saturday.
Bauchi police spokesman, Haruna Mohammed, confirmed that polling stations in nearby Kirfi were attacked on Sunday and election materials were destroyed.
A series of suspected attacks on polling stations in neighbouring Gombe state on Saturday killed at least seven.
Boko Haram leader Abubakar Shekau had vowed to disrupt the election, calling it "un-Islamic".
Source: Al Jazeera and agencies