Nigeria's main opposition presidential candidate Atiku Abubakar has boycotted an event to commit candidates to promote peace during what is expected to be tightly contested elections next year.

The peace pledge was signed by President Muhammadu Buhari.

It is not clear why Atiku Abubakar and his party, the People's Democratic Party (PDP), failed to sign the accord brokered by National Peace Committee, which is headed by former President Abdulsalami Abubakar.

The pact specifically mandates candidates to publicly speak against religious, ethnic and electoral violence.

In 2015, a similar accord is believed to have helped in ensuring peaceful polls which led to then-President Goodluck Jonathan accepting defeat.

But the boycott by the main opposition party and its presidential candidate is seen as a major blow to this year's accord.

However, Abdulsalami Abubakar said the absence of the main opposition candidate will not weaken the agreement, which was signed by more than 70 candidates.