Nigeria's President Goodluck Jonathan and the main opposition candidate, Muhammadu Buhari, have signed a pledge for peaceful elections in an effort to prevent violence days before the polls..

Thursday was the second time such a pledge was made in three months. The accord was signed in the presence of former UN Secretary-General Kofi Annan at a hotel in the capital, Abuja, and broadcast live on television.

Security is a major concern at Saturday's vote, with fears of both attacks by armed group Boko Haram on polling stations and clashes between rival supporters.

In 2011, hundreds of people were killed in violence after Jonathan beat Buhari to the presidency.

"Now that the campaigns have come to an end, we meet to renew our pledge for peaceful elections," read a document signed by the two men and made available to reporters.

"We therefore call on all fellow citizens of our dear country and our party supporters to refrain ‎from violence or any acts that may in any way jeopardise our collective vision of a free, fair and credible election."

The duo also pledged to "respect‎ the outcome of free, fair and credible elections".

The document was also signed by the chairman of the National Peace Committee Abdulsalami Abubakar, who like Buhari is a former military ruler.

It was also witnessed by Nigeria's most senior Muslim leader, the Sultan of Sokoto Saad Abubakar and the Roman Catholic Archbishop of Abuja, John Onaiyekan.

Jonathan and Buhari signed another pledge of non-violence in Annan's presence on January 14.

At that stage, elections were set for February 14, but the vote was subsequently delayed to March 28 because of violence tied to Boko Haram.

Source: Agencies