The People's Democratic Party (PDP) has said Jonathan has the right to run, because he was previously vice president on a joint ticket with northern President Umaru Yar'Adua, who died mid-way through his first term earlier this year.

But the party also said that it would uphold the principle of "zoning" and that other candidates were free to contest at its primaries, expected to be held in September.

"He is not likely going to run, simply because his party has retained the zoning of the presidency to the north for the next four years," the presidency source said, asking not to be named.

"Though his party said he can run despite the zoning, the party said this because they didn't want to offend him."

The source said Jonathan would make his intentions public before the end of August. Presidency officials declined comment.

"(He) is a man that always ensures equity and fair play, so he may allow the north to have their remaining four-year term if that will ensure peace and unity," the source said.

A decision by Jonathan not to run would come as a surprise to many in Africa's most populous nation. Never before has an incumbent leader, constitutionally allowed to seek re-election, withdrawn from a presidential race.

It could also lead to protests from his restive Niger Delta homeland, the centre of the mainstay oil and gas industry. Jonathan is Nigeria's first president from the Ijaw ethnic group, the largest in the vast wetlands region.