Nigerian President Muhammadu Buhari has been re-elected for a second four-year term, the Nigerian election commission says.
The 76-year-old defeated his main rival, former Vice President Atiku Abubakar, with a margin of nearly four million votes.
Mr Abubakar’s People’s Democratic Party (PDP) has rejected the result.
Turnout was 35.6 percent.
Delays and violence marred the run-up to Saturday’s poll but no independent observer has cited electoral fraud.
Mr Buhari’s All Progressives Congress (APC) won in 19 of the 36 states while the PDP was victorious in 17 states and in the capital, Abuja, according to the electoral commission (INEC).
“The new administration will intensify its efforts in security, restructuring the economy and fighting corruption,” Mr Buhari said after his victory was officially announced.
The APC had 15.2 million votes while the PDP had 11.3 million.
Some supporters of Mr Buhari took to the streets late on Tuesday in celebration.
Mr Buhari, a former soldier, led a military regime for 20 months in the 1980s and was first elected president in 2015, becoming the first opposition candidate to defeat an incumbent and win the presidency.
His record in office is mixed. Mr Buhari’s critics say the very attributes that won over voters four years ago – his strictness and inflexibility – have emerged as liabilities.
They accuse him of autocratic leanings as well as a disastrous tendency towards inaction.
Mr Buhari’s supporters can argue that he has largely delivered on campaign pledges such as tackling corruption and cracking down on Boko Haram.
But they may struggle to point to concrete achievements in other fields, such as fixing the economy.
Earlier on Tuesday, opposition PDP chair Uche Secondus called the count “incorrect and unacceptable”.
The party said counting should be stopped, alleging data from voter card readers had been manipulated.
The federal government accused the PDP of trying to “scuttle the polls” and prompt a constitutional crisis.
Some 130 people have been taken into custody suspected of electoral offences, reports say.