As many as 39 people have died in election-related violence in Nigeria, as the country awaits the results of this weekend's voting in what is forecast to be its tightest poll since the end of military rule in 1999.
Current President Muhummadu Buhari, 76, a former military ruler is seeking a second term on an anti-corruption platform.
He faces off against businessman Atiku Abubakar, 72, a former vice president who has promised to expand the role of the private sector.
The election was held on Saturday, but violence and problems with electronic voting machines meant voting continued in a small number of places before polls closed on Sunday.
The ballot was initially due to take place last week, but was postponed just hours before it was due to begin, with the authorities citing logistics.
Nigeria's 73 million eligible voters chose from a pool of more than 70 presidential candidates, although only those from the two main parties — Mr Buhari and Mr Abubakar — are seen as having a chance.
The President last year publicly denied social media claims he died and was replaced by a Sudanese clone, and also courted international controversy in the past by suggesting his wife "belongs in the kitchen".
The Situation Room — which represents more than 70 civil society groups — gave Sunday's figure of 39 deaths, citing data from Lagos-based consultancy SBM Intelligence.
In one incident, seven people were killed in a shootout between Nigerian army troops and a gang.
Mahmood Yakubu, chairman of the Independent National Electoral Commission (INEC), said an electoral official had been shot dead by unknown people.
The president's office declined to comment, while the opposition candidate Mr Abubakar condemned the violence in a statement.
The number of deaths reported by Sunday was below the final death tolls in previous elections in Africa's most populous country, but in the past most unrest has taken place after results were announced.
What's at stake?
A credible and relatively calm poll 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.
"From Tuesday onwards we should have a substantial number of results," said Festus Okoye, an election commission official.
The contest between Mr Buhari and Mr Abubakar, commonly called "Atiku", hinges on revamping an economy struggling to recover from its first recession in 25 years, which it slipped into in 2016 and emerged from in 2017.
Nearly a quarter of the workforce is unemployed, while the cost of living has also risen rapidly.
Mr Buhari has focused his campaign on rooting out corruption, but critics say there have not been any significant convictions in his first term.
Mr Abubakar has said he would aim to double the size of the economy to $900 billion by 2025.