Abubakar, a Muslim from the northern Hausa ethnic group, ran unsuccessfully for president as the opposition Action Congress candidate in 2007, polls which were won by fellow northerner, late President Umaru Yar’Adua.

An unwritten agreement in the ruling People’s Democratic Party (PDP) states that power should rotate between the Muslim north and Christian south every two terms, meaning the next president should be a northerner if the principle is maintained.

Jonathan, a Christian from the southern Niger Delta, has not yet said whether or not he plans to stand, but a bid would be controversial and he would need the support of northerners within the PDP to be guaranteed victory in the polls.

Abubakar’s declaration does not help his chances and increases the risk of division within the ruling party.

“This is not the time for a novice. This is not the time for ill-prepared leaders. This is not the time for risky experiments,” Abubakar said as he announced his bid, an apparent reference to concerns about ending the PDP “zoning agreement.”

“It is time for an experienced, committed and visionary leader to rescue our country from imminent collapse. I am that leader,” he said.

Former military ruler Ibrahim Babangida, known by his initials IBB, has also said he will seek the PDP’s nomination for the elections, raising the prospect of a fierce contest at the primaries.

Although Jonathan’s administration has made a raft of policy announcements in recent weeks which analysts say look more like campaign pledges, sources close to Jonathan say he is concerned about the implications of abandoning zoning.

The PDP has hedged its bets on whether it would fully endorse a Jonathan bid in primaries expected in September.

Jonathan, whose administration has made promises in the past few weeks on issues from improving electricity supply to building new roads, inherited the presidency when Yar’Adua died earlier this year part way through his first term.

The party said last week that Jonathan had the right to contest because he had come to power with northern President Yar’Adua in 2007 on a joint ticket and that he could legitimately seek to complete that term.

But it stopped short of giving him its full endorsement and said it upheld the principle of zoning.

Abubakar laid out five key priorities: creating jobs, improving power supply and infrastructure, fighting corruption and boosting security, education and health, and development in the restive Niger Delta oil region.

“Together we shall clean up and restore the environment of the Niger Delta, speed up the development of the area,” he said.

“Oil and gas prospecting does not have to be a death sentence for those who are fortunate to sit on vast amounts of energy resources.”

Jonathan has support from state governors — who form a powerful caucus in the PDP — in the south and the central Middle Belt, where the backbone of the army are from. But northern Muslim governors have acknowledged his right to stand while stopping short of endorsing him.