OFFICIAL: How Nigeria voted to re-elect Buhari as President

Nigerian President Muhammadu Buhari has been re-elected for a second four-year term, the 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%.

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.

Overall, the APC got 15.2 million votes while the PDP received 11.3 million.

Mr Buhari swept the north, while Mr Aububakar did better in the south and east.